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Unit 3 Physics - Energy

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Things to remember in this chapter…..

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3.1 Properties of Energy

Properties of Energy

• By ________________________ and _______________________ about the effects of energy, scientists have found that

• Energy can cause ___________________________ in a system

• There are different forms of energy, with different ________________________________

• These forms of energy can be ________________________________________________

• Different ______________________________________ contribute to different forms of energy

Forms of Energy

There are two main types of energy:

• _________________________________: the energy of motion

• _________________________________: the stored energy of an object as a result of its

condition or its position

• The SI unit of kinetic energy is the _________________, abbreviated _______

Kinetic Energy

• Kinetic Energy is the energy of an object as a result of its _______________

• the name kinetic from the Greek word ________________ meaning motion

• kinetic energy can be _________________________ between objects when they collide

or _________________________into other forms of energy

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Types of kinetic energy:

1. ________________________________: energy of an object that is in motion

2. ________________________________: energy of electromagnetic waves from a source

3. ________________________________: energy of random motion of particles

4. ________________________________: energy of vibrations of particles

5. ________________________________: energy of electrons moving along a wire

Potential Energy

• Potential Energy is the energy ___________________________________________

because of their position, stresses inside of the object, or their charge

• potential energy is stored inside an object and is not useful until it is __________________

into another type of energy _______________________

• in other words, it is the __________________________________ another type of energy

Types of potential energy:

1. ______________________________: energy stored in a stretched or compressed object

2. ______________________________: energy stored in chemical bonds

3. ______________________________: energy due to the position of an object

4. ______________________________: energy stored in the nucleus of an atom

5. ______________________________: energy is stored by a separation of + /- charges

6. ______________________________: energy stored in a magnetic field

Law of Conservation of Energy

• The law of conservation of energy states that energy is neither created nor destroyed, but

is _______________________ from one form of energy to another or ________________

from one object to another.

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• When energy is ____________________, the energy ______________________________

that is originally was.

• When energy is ____________________, the energy changes from

__________________________________________________.

• When energy transformations occur, some of the energy is _________________________

that is not useful but no energy is ever lost

Energy Transfer or Transformation

• Chemical potential energy is ______________________________ into electrical energy

• Electrical energy then ____________________________ along the wires of the flashlight

to the light bulb

• Electrical kinetic energy is _________________________ into light (radiant energy) but

some of it is also transformed to ______________________ heat (thermal energy)

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3.1 Properties of Energy - Assignment

1. Why can it be a challenge to observe energy directly? What can you observe?

2. What is the difference between kinetic and potential energies?

3. Identify the following as either potential energy or kinetic energy.

4. What is the Law of Conservation of energy?

5. How do energy transfer and transformation differ? How are they similar?

Scenario Type of energy a) A bicyclist coasting down a hill reaches the

bottom of the hill.

b) An amusement park ride stops at the top.

c) A bowling ball rolling down the alley.

d) An archer with his bow drawn.

e) Sitting in the top of a tree.

f) A bowling ball sitting on the rack.

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6. Identify four types of energy in the photo. Classify each type of energy as either kinetic or potential and explain your answer in each case.

7. Explain why thermal energy is a form of kinetic energy

8. Identify an energy transformation that occurs in your daily life.

9. Identify an energy transfer that you experience every day.

10. Explain how the energy transformation you described differs from the energy transfer.

11. Why is no process of energy transformation 100 percent efficient?

12. Describe how chemical potential energy can be transformed into kinetic energy of a soccer ball. Begin with the muscles of a leg and follow the path to the motion of the ball.

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3.2 Kinetic Energy

Mechanical Kinetic Energy

• In this class we will focus on _____________________________________.

• This is energy due to an object with mass ____________________________

• __________________________ can affect different forms of kinetic energy.

Mass

• The __________________________________ in an object defines its mass

• mass of an object does not change unless something is ________________ or

_____________________ to it

• the SI unit of mass is the ____________________, abbreviated _______

Velocity

• all objects have a _________________________ relative to other objects

• when objects _________________________________, they have a velocity

• the more their position changes every second, the ____________________ their

velocity

• the SI units of velocity are _______________________, abbreviated ______

Kinetic Energy

• Imagine a truck driving ___________________________

• The ___________________________________ so it has kinetic energy

• What physical quantities would determine the kinetic energy?

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Mechanical Kinetic Energy Equation

• Mechanical kinetic energy can be calculated from physical quantities and the

following equation:

Ek =

m =

v =

• Remember from math that there is a correct order of operations ____________

which means we need to:

o __________________ the velocity first

o then multiply ___________________________.

Example 1: A 1,200 kg car is travelling at 28.5 m/s, what is its kinetic energy?

Scientific Notation

• 4.5 x 103 = move the decimal to the right =

• 4.5 x 10-3 = move the decimal to the left =

• 2.43 x 104 =

• 2.43 x 10-2 =

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Significant figures

• In science we round the final answer to the same number of significant figures as

the original value with the ________________________ of significant figures.

• For example 3.2 (____ significant figures) x 10.234 (___ significant figures) =

32.7488 rounds to _____ (___ significant figures)

• 143.1 (___ significant figures) x 1.2 x103 (____ significant figures) = 1.431x1200 =

1717.2 = ________ (___ significant figures)

Example 2: What is the EK of a baseball with mass 0.152 kg thrown at 32 m/s?

Other versions of the formula

• The formula can be changed around algebraically to solve for mass or velocity

like this:

With the velocity equation, solve everything inside the square root before you take the root.

With the mass equation, don’t forget to square the velocity first.

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Example 3: A 46 kg cheetah has a kinetic energy of 15,500 J, how fast is it running?

Example 4: What is the mass of a peregrine falcon flying at 88.9 m/s with a kinetic energy

of 1780 J?

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3.2 Kinetic Energy - Assignment

1. A girl is riding her bike at a velocity of 12 m/s. She weighs 55 kg and her bike weighs 22 kg. What is the kinetic energy of the girl and her bike?

2. Two objects were lifted by a machine. One object had a mass of 4 kg, and was lifted at a velocity of 2

m/s. The other had a mass of 2 kg and was lifted at a velocity of 3 m/s. Calculate which object had more kinetic energy while it was being lifted.

3. A moving dog with a mass of 34 kg has a kinetic energy of 25 J. How fast is the dog running? 4. A falling elephant with a velocity of 35 m/s has a kinetic energy of 1.50 x 105 J. What is the mass of

the elephant?

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5. If a falling water droplet travels at 11 m/s and has a kinetic energy of 9.6 x 10–3 J, what is the mass of the droplet?

6. A box hits the ground with 3.2 x 104 J of kinetic energy. If the box was traveling at 40.0 m/s when it

hit, what must the mass of the box be? 7. Schwab is shot out of a cannon. If his mass is 68 kg and he has a kinetic energy of 706 J, how far

does he travel in the first second after leaving the cannon?

Solutions (1) EK = 5,500 J (2) EK of 4 kg object = 8 J, EK of 2 kg object = 9 J The 2 kg object had more kinetic energy while it was being lifted (3) v = 1.2 m/s (4) m = 240 kg (5) m = 0.00016 kg (6) m = 40 kg (7) v = 4.6 m/s

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3.3 Potential Energy

Gravitational Potential Energy

• In this class we will focus on __________________________ potential energy.

• This is _____________________________due to its position above the Earth.

• Imagine a boulder on a cliff above Wile E. Coyote:

o It has the ____________________________ and transfer this energy onto

him.

o What physical quantities would determine the potential energy?

o

• Gravitational potential energy can be calculated from physical quantities and the

following equation:

EG =

m =

g =

∆h =

• The formula can be changed around algebraically to solve for mass or height like

this:

• it is easiest to solve the denominator first, and then divide the EG by that result

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Examples

1. What is the potential energy of a 62 kg man when he walks a 415 m high tightrope?

2. What is the EG of a penny with mass 0.00235 kg held at 276 m on the top deck of the Eiffel

Tower?

3. A 6.21 kg vulture has a potential energy of 4.4 x 105 J, how high is it soaring?

4. What is the mass of a skydiver waiting to jump at 3800 m with a potential energy of 3.26 x

106 J?

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Conservation of Energy

• Recall that the Law of Conservation of Energy states that energy can neither

____________________ nor destroyed, but it can be ___________________ from

one kind to another

• Imagine a ball being thrown up into the air:

• As the ball travels ___________ EK is converted into EG

• As the ball falls _____________ EG is converted into EK

• This is similar to a pendulum:

Solving energy transformation problems

• To solve questions with energy transformations, all the __________________ will

be converted into _______________________

• This means that we can put the ___________________________ to solve for one

of the physical quantities

• Solve for the ____________________________________________ and then put in

the numbers you are given

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Examples

5. A baseball is thrown straight upward with a velocity of 5.63 m/s, how high does it travel?

6. A 15 kg coyote is at the top of a 205 m cliff. What velocity will it reach if it misses the

roadrunner and falls to the ground?

7. A snowboarder starts at rest and travels down a hill 45 m high as shown. How fast will the snowboarder be travelling at the bottom of the hill?

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3.3 Potential Energy - Assignment

1. A box with a mass of 30 kg is sitting on a shelf 3 m above the ground. What is its potential

energy?

2. A rubber ball has 150 J of potential energy and a mass of 0.254 kg. How high is the ball off the ground?

3. A pole vaulter at the top of her jump is 5.90 m above the ground. If her potential energy is

4942 J, what is her mass? 4. In 1993, Cuban athlete Javier Sotomayor set the world record for high jump. If his potential

energy at the top of the jump was 1970 J, and his mass was 82.0 kg, how high did he jump?

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5. A 72 kg pole-vaulter running at 8.4 m/s completes a vault. If all of her kinetic energy is transformed into potential energy, what is the maximum height of her vault?

6. A 650 kg truck is parked at the top of a 42.0 m hill. How fast will the truck be moving when it

reaches the bottom of the hill?

7. A handgun is fired very foolishly straight upwards into the air. If the bullet leaves the muzzle

of the gun with a velocity of 240 m/s, how high will the bullet travel? 8. A boulder with a mass of 682 kg is resting on the edge of an 85 m cliff. If it falls off the cliff

and lands on top of the coyote, how much kinetic energy will it have and what is its velocity as it strikes the ground?

Solutions: (1) EP = 900 J (2) h = 60 m (3) m = 85.4 kg (4) h = 2.45 m (5) h = 3.6 m (6) v = 28.7 m/s (7) h = 2,900 m (8) EG = 569, 000 J, v = 41 m/s

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Extra practice

1. In the future a can of spinach with mass of 0.14 kg loses 28 J of potential energy falling off of a shelf on Mars (g=3.8m/s2). How high above the surface of Mars was the can before it fell?

2. In a lab activity, a group of students measures the velocity of a model car. The car’s starting position at the top

of the ramp was 1.24 m above the floor. a. If the model car had 2.35 J of potential energy at the top of the ramp, what is its mass?

b. If the same car is moving at 2.5 m/s what is the kinetic energy of the car?

3. a. The movement of a rollercoasters car has been graphed below. If the rollercoaster car and the people

inside had a total mass of 535 kg, what is the potential energy of the rollercoaster car at time 4 s?

b. What is the velocity of the same 535 kg car when it reaches the bottom of the track at time 7 s?

Solutions: (1) h = 53 m (2) a ) m = 0.19 kg b) EK = 0.60 J (3) a) EG = 524,000 J b) v = 44.3 m/s

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3.4 Radiation

Protons & Neutrons

• Standard notation

o Atomic number = ____________________________

o Mass number/atomic mass = _____________________________

• Each element has different # of protons

o Change the protons, change the ____________

o Change the electrons create ____________

o Change the neutrons create ____________

Isotopes

• An isotope of an element has the same __________________, but a different

____________________________.

o Reason: same number of __________________, but a different number of

_____________________

• Isotopes of an element have the ________________________________, but may have

different ______________________________

• Isotopes exist in different _________________ in nature

• Ex. Carbon (all C have 6 Protons)

o > 99% of C atoms have 6 Neutrons = Carbon-____

o < 1 % of C atoms have 7 Neutrons = Carbon-____

o trace amounts of C have 8 Neutrons = Carbon-____

(radioactive, formed by cosmic rays)

• Atomic mass on Periodic Table is an ____________________________

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• Isotopes can be written in _________________________________.

• For example

o uranium-238

o carbon-14

Ideal neutron to proton ratio

• For every _________________ (number of _______________) there is an ideal

______________________________________________.

• Any deviation from this ratio decreases the _____________________________________.

• In small atoms the neutron to proton ratio is ___________

• In ___________ atoms _________________________ are needed since the __________

(all + charged) start to ____________ each other and more neutrons are needed to

_______________________________________ (protons and neutrons attract).

• For example uranium-238 has 146 neutrons and 92 protons or a ratio of about ______.

• When the neutron to proton ratio for a nucleus is too ____________________ from the

_______________________________ the nucleus is ______________.

• It is thus ______________________and will __________________________.

• The decay process results in a nucleus that is ______________.

Radiation

• Radiation is the spontaneous emission of _________________________ from the nucleus

of an ___________________ atom.

• Radiation comes in 3 types:

o ______________________ decay

o ______________________ decay

o ______________________ decay

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Alpha decay

• Alpha decay: a nuclear reaction that emits ______________________

(_________________)

• The new nucleus has ___________________________________________.

• When an atom changes the number of protons it changes into a different element this is

called ___________________.

o Loses _____ protons and _____ neutrons

o Mass _______, Atomic number _________, new element

Beta decay

• Beta decay: a nuclear reaction that emits ____________________________ (electrons)

• A neutron breaks apart into a _______________________________

• The new nucleus has one less ______________ and one more ___________

(transmutation occurs).

o Gains ______ proton , loses ______ neutron

o Mass __________, Atomic number ___________, new element

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Gamma decay

• Gamma decay: a nuclear reaction that emits ____________________ (energy

___________, No transmutation occurs)

• The ____________________________ that is undergoing the decay has a “*” to represent

an ___________________________.

o Emits energy only, no particles, mass or charge

• Since no particles are lost, mass & atomic # _________________

• _____________________ occurs

Summary

• Alpha: loses _______________ and ________________

o Mass goes __________________, atomic number goes ________________

• Beta: neutron breaks into ______________________

o Mass stays the _____________ , atomic number goes _____________

• Gamma: _____________ is given off in a ray

o Mass and atomic number _______________________________

*

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Examples

Write an equation for the following:

1. Protactinium-231 emits an alpha particle

2. Einsteinium-252 emits a beta particle

3. Berkelium-247 emits a gamma particle

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(Name for hydrogen with 1 neutron)

3.4 Radioactivity - Assignment

1. Complete the following table:

2.

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3. The following radioactive parent nuclei emit a beta particle. Predict the products.

4. What is lost from the atom in each case? How does mass and atomic number change?

Alpha decay:

Beta decay:

Gamma decay:

5. What makes an atom radioactive?

6. Why does emitting alpha and beta particles make an atom more stable?

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7. State whether the following descriptions apply to alpha, beta, or gamma radiation: a. Has a negative charge

b. Is a helium nucleus

c. Is stopped by a few sheets of paper

d. Has the most mass

e. Easily penetrates skin and tissue

f. Is given off as a ray

g. Is stopped by aluminum

7. Write the following equations:

a. Palladium-106 emits an alpha particle

b. Thorium- 233 emits a beta particle

c. Americium-244 emits a gamma ray

d. Hassium-265 emits a beta particle

e. Cerium-140 emits a gamma ray

f. Europium-152 emits an alpha particle

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3.5 Fission and Fusion

Nuclear fission

• _____________ elements can ___________________ into smaller elements.

• Larger elements are generally ___________________ so the addition of one

_______________ can be enough to cause them to ____________________.

• When elements break apart they release ________________.

• Nuclear fission: a process in which a ________________ is split into smaller,

lighter nuclei with the _____________________

• A single fission reaction usually results in a ____________________ of many

further reactions.

• ______________________ is more than 1,000,000 times greater than energy from

chemical reactions

Nuclear Power Generation

• To produce a _____________amount of energy, ____________________________

must happen

• A chain reaction occurs when the _______________ of one fission reaction

__________________________________.

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• A ____________________ starts the fission, but additional neutrons released

_______________ the chain reaction

• Produces very large amount of ______________

• Uranium-235 is used in nuclear reactors as this ______________ of uranium is

___________________ and the addition of _______________ starts a chain

reaction to produce lots of energy.

• Nuclear reactors ___________________ of the chain reaction and produce

_____________________, which can be converted into _____________energy.

• Nuclear reactors Supply ________________ of world’s electricity

Nuclear Waste

• A ______________ of nuclear energy is that the waste products such as

____________ (mass of 83 in periodic table) and _____________ (mass of 137)

have ____________________ and are thus radioactive. They must decay over time

by emitting alpha, beta and gamma _______________ so their nuclei can return to

a ______________________________.

• The reason _____________________ cause such extended trouble is that the

________________________ can take a long time.

• Decay of a single radioactive nucleus is _________________________________.

• We know it will decay but not exactly when.

• The process is measured in ________________: the amount of time when

_____________________ in a sample will have undergone decay and

_____________ releasing __________________.

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Nuclear fusion

• Nuclear fusion: a process in which ___________________ combine, or fuse, to

form a slightly _____________ nucleus

• It requires ________________________.

• It occurs in the Sun and other stars.

• It does _____________produce radioactive materials.

• When atoms fuse together _______________________ of energy are released.

• ________________________ needed to start fusion (must overcome repulsion) so

fusion __________________ not possible yet since _______________________ to

create necessary high temps then is ___________________ during fusion.

• Research continues in this area, since fusion produces _____________________

Examples

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3.

4. What is the half-life of this sample?

b. what amount of carbon-14 is left after 20

thousand years?

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3.5 Fission and Fusion - Assignment

1. Complete the following nuclear equations:

2.

3. One possible outcome of the fission reaction of uranium is the production of strontium-90 and xenon-143 along with three neutrons and energy. Write the nuclear equation for this reaction beginning with the addition of a neutron to a uranium-235 nucleus.

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4.

5. Why must two nuclei be moving at high speeds for nuclear fusion to occur?

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6. How are nuclear fission and fusion similar?

7. How are nuclear fission and fusion different?

8. Nitrogen-13 decays to produce carbon-13. A laboratory sample contains 500 000 nitrogen-13 atoms. Use the decay curve for the sample over time to answer the following questions

(a) How many nitrogen-13 atoms will be left after 15 min?

(b) How many nitrogen-13 atoms will be

present after 25 min? (c) What is the half-life of nitrogen-13? (d) How many nitrogen-13 atoms will be

present after 40 min?

9. Cesium-124 has a half-life of 31 s. A sample of cesium-124 in a laboratory has an initial mass of 20 mg. (a) Determine the amount of time it will take for the sample to decay to 5 mg. (b) How many cesium-124 atoms will be present after 25 s? (c) What is the half-life of cesium-124?

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Physics Unit 3 Review Assignment

1. Compare kinetic energy and potential energy. How are they different?

2. The photo shows a scene at the Capilano Suspension Bridge Park in Vancouver. Identify as many forms of energy as you can that are present in or that could be inferred from the photo. Identify

each form as kinetic or potential.

3. Explain how energy is transformed and transferred to bring a pot of water to a boil on a stove.

4. A scientist has developed a building material that reduces the damage caused by earthquakes. Use

the concepts of energy transfer and/or transformation to suggest how this material might work.

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5. Only as much as 10% of the electrical kinetic energy that is used by a halogen light bulb is transformed into light energy. What happened to the remaining 90% of the energy?

6. A 54 kg skier, including equipment, stands at the top of a black diamond ski run. The vertical

distance to the bottom of the run is 420 m. What is the gravitational potential energy of the skier relative to the bottom of the ski run?

7. A satellite has a mass of 689 kg and travels at a speed of 27 000 km/h (7500 m/s). How much mechanical kinetic energy does the satellite have?

8. A bowling ball is rolling down the lane at 2.8 m/s. If it has a mechanical kinetic energy of 25.5 J, what

is its mass?

9. A skateboarder starts at rest and travels down a 50 m ramp. How fast will she be traveling at the bottom of the ramp.

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10. What is a radioactive isotope?

11. Lead-208 a. Write the symbol (in standard notation):

b. Number of protons?

c. Number of neutrons?

12. The following emits a alpha particle, predict the products.

20884 Po →

13. The following emits a beta particle, predict the products. 9039Y →

a. Electrons do not exist in the nucleus of atoms, yet this equation seems to indicate that an electron came from a nucleus. Explain why this is not a contradiction.

14. The following emits a gamma ray, predict the products. 137 *

56 Ba →

a. What does the star (*) in this equation indicate?

b. Why might you expect this reaction to occur immediately after another nuclear reaction?

15. Write the following equation: Thorium-233 emits an alpha particle

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16. Consider the following nuclear equation.

a. Fill in the blank numbers b. Name the type of nuclear reaction that is described by this equation.

c. Explain the function of the neutron on the left side of the equation.

17. Consider the following nuclear equation.

a. Fill in the blank numbers. b. This equation describes a nuclear reaction that is an example of what general type?

c. Where would you expect to find this type of reaction occurring?

d. Describe the conditions that are necessary in order for this type of reaction to occur.

e. If scientists found a way to control this type of reaction for the commercial production of power, why would it be advantageous compared to modern nuclear reactors?

18. What is the half life of the following Isotope.