Date post: | 21-May-2015 |
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Mechanical Energy
K Warne
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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).
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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
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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)
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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
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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)
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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
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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
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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
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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
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Pendulum Investigation
• Plan an investigation to determine all the factors which affect the time taken for a pendulum to complete one full swing. (Period)
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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
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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