energy

EnergyWhat do they all have in common?

Energy • Defined as the ability to cause change!!• Revisit the previous slide and explain how

each of these has the ability to cause change!!

2 Types of EnergyKinetic Energy• Energy of motion.– In order to have

Kinetic energy an object must be in motion(It must have a velocity!!

Potential Energy• The energy of position

or condition.• Several kinds of

Potential Energy:1. Gravitational PE2. Elastic PE3. Chemical PE4. Nuclear PE

Types of Potential Energy

• Gravitational Potential Energy(Peg) is the potential energy an object has due to its height. – The higher an object, the more potential it has to

cause change!!Mr. Eidson

Mr. Rodgers

• Elastic Potential Energy is the potential energy an object has due to being stretched or compressed.

Types of Potential Energy

• Chemical Potential Energy is the potential energy something has because of its chemical makeup!!

Types of Potential Energy(cont.)

Sodium tossed into pond!

• Nuclear Potential Energy is the potential energy of the particles inside an atomic nucleus.

Types of Potential Energy(cont.)

Kinetic Energy

Where:

KE = kinetic energy in Joules(J)m = mass in kilograms(kg)v = velocity in m/s

James Prescott Joule 1818-1889

Ex. A 1500 kg car moves down the road at 12 m/s. How much kinetic energy does the car have?

Given:

m = 1500 kgv = 12 m/sKE = ?

KE = ½(1500kg)(12 m/s)2

KE = 108,000 J

Ex. A 350 kg boulder is rolling down a hill at 17 m/s. How much kinetic energy does the boulder have?

Given:

m = 350 kgv = 17 m/sKE = ?

KE = ½(350kg)(17 m/s)2

KE = 50,575 J

A 1.5 kg football is thrown with a velocity of 15 m/s. What is the kinetic energy of the football?A. 11.25 JB. 22.5 JC. 168.8 JD. 337.5 J

A 2000 kg truck is moving down the highway at 8 m/s. What is the kinetic energy of the truck?A. 8000 JB. 16,000 JC. 64,000 JD. 160,000 J

Ex. A 3000 kg racecar has 200,000 J of kinetic energy as it moves around the track. Determine the velocity of the racecar?

Given:

m = 3000 kgv = ?KE = 200,000 J

Ex. A 25 kg rock is thrown with a velocity of 2 m/s. What happens to the kinetic energy of the rock if the velocity is doubled?

Given:

m = 25 kgv = 2 m/sKE = ?

KE = ½(25kg)(2 m/s)2

KE = 50 J

KE = ½(25kg)(4 m/s)2

KE = 200 J

KE increases by a factor of 4!!?

Gravitational Potential Energy(PEg)

PEg = mgh = FghWhere:

PEg = Gravitational Potential Energy in Joules(J)m = mass is kilograms(kg)g = acceleration due to gravity(9.80 m/s2)h = height in meters(m)Fg = weight in Newtons(N)

If there are 2 equations,

how do I know which one to

use??

I don’t know, we should

probably ask Hillary? She thinks she

knows everything!!!

Well, if you’re given the mass(in kg), use

PEg = mgh

And if you’re given

weight(in N), use

PEg = Fgh

Ex. A 450 kg boulder rests on the edge of a 120 m high cliff. Determine the gravitational potential energy of the boulder.

Given:

m = 450 kgh = 120 mg = 9.80 m/s2

PEg = ?

PEg = mgh

PEg = 450(9.80)(120)

PEg = 529,200 J

Ex. A 90 N flowerpot sits on the edge of a 14 m high window. How much potential energy does the flowerpot have?

Given:

Fg = 90 N h = 14 mPEg = ?

PEg = Fg h

PEg = 90 N(14 m)

PEg = 1,260 J

Ex. To what height would you have to lift a 25 kg barbell to give it 612.5 J of potential energy?

Given:

m = 25 kgPEg = 612.5 Jg = 9.80 m/s2

A 4500 kg boulder rests on the edge of a 40 m high cliff. What is the potential energy of the boulder?A.180,000 JB. 1,764,000 JC. 260,000 JD.2,390,000 J

A 400 N box rests on a 2.5 m high cliff. What is the potential energy of the box? A. 1000 JB. 4800 JC. 9800 JD. 14,200 J

Is it possible for one type of energy to change to another type of energy?

Consider the picture to the left:

At point A, what type of energy does the ball have? Potential Only WHY?At point B, what type of energy does the ball have?Both PE and KE WHY??At point C, what type of energy does the ball have?KE only WHY?

How did this happen?

Tomorrow:You will design your own lab to answer the

following question……..“Is there a relationship between Gravitational Potential Energy and Kinetic Energy for a ball tossed into the air(A Free-Falling Body)?

You will state a hypothesis(after discussion with your group), design an investigation, analyze data, state a conclusion!!!

Can other types of energy change?

WHY?

Where is PE and KE highest and lowest?

Rank Potential Energy from high to low!A-----C-------E----------D--------B

Rank Kinetic Energy from high to low!B------D------E----------C--------A

Which Skier has the highest Potential energy?

Which skier has the highest kinetic energy?

Which Skier is moving the fastest?

Where is the potential energy the greatest?

Where is the potential energy the least?

Where is the kinetic energy the greatest?

Where is the kinetic energy the least?

Which rock is moving the fastest?

Law of Conservation of Energy• As long as no unbalanced forces act on a

system of objects, the total energy in a system will remain the same.

• Energy may change form, but it cannot be created nor can it be destroyed!!

Mechanical Energy remains Constant:

• Total Potential and Kinetic energy.– ADD THEM UP!!