energy

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Mechanical Energy

K Warne


Mass & WeightMass:• This is a measure of

the amount of ................(stuff) that makes up a body.

Weight:

• This is the ................ exerted by gravity exerted on a body’s mass by the earth (planet).


Mass & Weight - tableInvestigation: To determine the relationship between an object’s mass and weight.

Method: We are going to weigh a number of different masses on a spring balance.

We will record the mass and weight in each case. (In a table.)

We will then analyse the results to see if any patterns (relationship) can be seen.

Mass/kg Weight/N


Mass vs Weight - Graph

0

0.5

1

1.5

2

2.5

3

0 0.1 0.2 0.3 0.4

Weig

ht/

N

Mass/ kg

Mass & Weight

From the graph we can see that the weight rises as the mass is increased. The straight line indicates a direct proportion between mass and weight. (Double the one the other will also double).

Line corrected for systematic error scales were not zero’d correctly.

Graph should pass through (0;0)


Work

• The unit of work is N.m called a Joule(J).• The joule is the amount of work done when a force of 1N

acts over 1m.1J=

• Work is a ………….quantity.• From the formula we see that if there is ……………. then

there is no work done.• If the displacement is …………………………. to the

force then there is no work done either.• Q How many joules of work does it take to lift your body

up a 4m staircase?

Work is done when a ………………force is applied to an object and causing the object to be ………….. in the …………. of the

force.

W = ...............

4m


Energy• Energy is the …………………. to do work.• Energy is a scalar quantity and measured in

……………….• Energy is ……………….. to an object when work is

done on it by a resultant force.• The energy transferred is ………………. to the

work done.• A 200N force moves a block (M) over a distance of

5m. How much energy is required?

Force – F (200N)M mDisplacement s (5m)

V (10m.s-1)


Gravitational Potential Energym Potential energyPotential energy is the energy a body has

because of its ...................................... or …................….................

Any object that is above the ground has the POTENTIALPOTENTIAL to fall Down.

It has potential energy (Epotential energy (EPP)) - given by:

EEpp = ………………. = ……………….where;

m = the …………. of the object (kg)g = the ……………….. due to gravity (10m/s2)h = ………………. above the ground (m)

How much energy is gained by a 50g tennis How much energy is gained by a 50g tennis ball which is hit 6m up into the air?ball which is hit 6m up into the air?

g (9.8m/s2 )

EK PotentialEnergy (mgh)

m

m

Ep PotentialEnergy GAINED

Object could fall downObject could fall down

h


Kinetic Energy (Ek)m

KINETIC ENERGY (EKINETIC ENERGY (EKK) is the energy a body has when it is ) is the energy a body has when it is

………………………...………………………...

The kinetic energy is given by:

Ek = ………………………where;

m = the ………………… of the object (……………)v = the ……………………… (speed) the object is moving (…………..)

What is the kinetic energy of a 1 tonne car moving at 60km.hWhat is the kinetic energy of a 1 tonne car moving at 60km.h -1-1??

EEKK Kinetic Energy = …………..……. Kinetic Energy = …………..…….

m


VelocityYou may be asked to rearrange the kinetic energy formula so you can calculate the mass of a moving object or the velocity of a moving object, if you do not think you can rearrange the formula in the examination, remember the rearranged formulae.

Do you know what the two formula would be for mass and velocity?

Mass = 2Ek

(v)2

Velocity = 2Ek

m


Mechanical Energym Any object that is above the ground

has the POTENTIAL to fall Down.

The potential energy EP =mgh (Height) lost would be converted converted

into speed (kineticinto speed (kinetic energy) Eenergy) EKK..

EEpp(…….) = E(…….) = Ekk(………..)(………..)

If the object is If the object is liftedlifted up then it up then it gainsgains potential energy.potential energy.

At any time the sum of the KINETIC At any time the sum of the KINETIC and POTENTIAL is called the and POTENTIAL is called the ……………………….. ENERGY - ……………………….. ENERGY - and it stays …………..and it stays …………..

Ep PotentialEnergy LOST

EEKK ……. = E ……. = Epp …….. ……..

E = Ep + Ekm

4kg

8m8m

Ep = mgh

Ek = 320J

E = Ep + Ek

= …….. = ………

E = Ep + Ek

= ……… = ……….

4mE = Ep + Ek

= ………. = ……….

Ep = 0

Ek = 0J


Pendulum Investigation

• Plan an investigation to determine all the factors which affect the time taken for a pendulum to complete one full swing. (Period)


A pendulum• A person of 60kg is lifted to a height of 30m on a slingshot

pendulum and then released what is its maximum speed?

m

h

ETop = Ep + EK

= mgh + 1/2mv2

= (60)(10)(30) + 0 = 18000J

Total Mechanical Energy(Top)

EBottom = Ep + Ek

= mgh + 1/2mv2

18 000 = 0 + 1/2 (60)v2

v2 = 18000/30 = 600 v = 600 = 24.5 m.s-1


Hi -

This is a SAMPLE presentation only.

My FULL presentations, which contain loads more slides and other resources, are freely available on my resource sharing website:

www.sciencecafe.org.za

(paste into your browser if link above does not work)Have a look and enjoy!

Keith Warne

energy

Education

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mass weight mass

energy energyis

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haspotential energy

gravitational potential

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