Download Energy, Work, and Power

Energy
 Makes things happen. Takes many different forms and
changes readily from one form to another.
Energy
 Makes things happen. Takes many different forms and
changes readily from one form to another.
 Active Energy – effects easily seen or detected.
-
Energy
 Makes things happen. Takes many different forms and
changes readily from one form to another.
 Active Energy – effects easily seen or detected.
- Kinetic energy (Ek – the energy of an object when its
moving)
Energy
 Makes things happen. Takes many different forms and
changes readily from one form to another.
 Active Energy – effects easily seen or detected.
- Kinetic energy (Ek – the energy of an object when its
moving)
- Light energy
Energy
 Makes things happen. Takes many different forms and

-
changes readily from one form to another.
Active Energy – effects easily seen or detected.
Kinetic energy (Ek – the energy of an object when its
moving)
Light energy
Heat energy
Energy
 Makes things happen. Takes many different forms and

-
changes readily from one form to another.
Active Energy – effects easily seen or detected.
Kinetic energy (Ek – the energy of an object when its
moving)
Light energy
Heat energy
Sound energy
Potential energy
 Forms of energy which are stored and only have an
effect when they are changed to active energy (Ep)
Potential energy
 Forms of energy which are stored and only have an
effect when they are changed to active energy (Ep)
- Chemical potential energy – changed to active energy
by chemical reactions.
Potential energy
 Forms of energy which are stored and only have an
effect when they are changed to active energy (Ep)
- Chemical potential energy – changed to active energy
by chemical reactions. Food, fuels, and explosives
contain chemical potential energy.
Potential energy
 Forms of energy which are stored and only have an
effect when they are changed to active energy (Ep)
- Chemical potential energy – changed to active energy
by chemical reactions. Food, fuels, and explosives
contain chemical potential energy.
- Elastic potential energy – energy stored when a
material is stretched or compressed.
Potential energy
 Forms of energy which are stored and only have an
effect when they are changed to active energy (Ep)
- Chemical potential energy – changed to active energy
by chemical reactions. Food, fuels, and explosives
contain chemical potential energy.
- Elastic potential energy – energy stored when a
material is stretched or compressed. It is changed to
active energy when the tension is released.
Potential energy
 Forms of energy which are stored and only have an
effect when they are changed to active energy (Ep)
- Chemical potential energy – changed to active energy
by chemical reactions. Food, fuels, and explosives
contain chemical potential energy.
- Elastic potential energy – energy stored when a
material is stretched or compressed. It is changed to
active energy when the tension is released.
- Gravitational potential energy – energy that is gained
when something is lifted up.
Potential energy
 Forms of energy which are stored and only have an
effect when they are changed to active energy (Ep)
- Chemical potential energy – changed to active energy
by chemical reactions. Food, fuels, and explosives
contain chemical potential energy.
- Elastic potential energy – energy stored when a
material is stretched or compressed. It is changed to
active energy when the tension is released.
- Gravitational potential energy – energy that is gained
when something is lifted up. This energy is changed to
active energy when the object falls down.
Potential energy
- Electrical energy – energy that is stored in a power
source (battery).
Potential energy
- Electrical energy – energy that is stored in a power
source (battery). This energy is changed to active energy
when the circuit is switched on.
Potential energy
- Electrical energy – energy that is stored in a power
source (battery). This energy is changed to active
energy when the circuit is switched on.
- Nuclear energy – energy that is stored in a nucleus.
Potential energy
- Electrical energy – energy that is stored in a power
source (battery). This energy is changed to active
energy when the circuit is switched on.
- Nuclear energy – energy that is stored in a nucleus.
Changed to active energy in nuclear reactors or atomic
bomb explosions.
Energy
 All forms of energy are measured in joules (symbol J)
Energy
 All forms of energy are measured in joules (symbol J)
 One joule is a very small amount of energy, so kilojoule
is often used kJ – 1000J = 1kJ
Questions:
1.
a)
b)
c)
d)
e)
Give an example of something that has:
Increasing kinetic energy
Decreasing heat energy
Decreasing chemical potential energy
Increasing elastic potential energy
Decreasing gravitational potential energy
Questions:
2. What type of energy is stored in:
a) An unlit firework?
b) An inflated balloon?
c) A hamburger?
d) A battery?
e) A child at the top of a playground slide?
Gravitational potential energy
 All to do with the height of an object – when height of
an object changes, its gravitational potential energy
changes.
Gravitational potential energy
 All to do with the height of an object – when height of
an object changes, its gravitational potential energy
changes.
Ep = mg
h
Gravitational potential energy
 All to do with the height of an object – when height of
an object changes, its gravitational potential energy
changes.
Ep = mg h
 Where
Ep is the increase in gravitational potential
energy in joules (J)
Gravitational potential energy
 All to do with the height of an object – when height of
an object changes, its gravitational potential energy
changes.
Ep = mg h
 Where
Ep is the increase in gravitational potential
energy in joules (J)
 M = mass in kg of the object being lifted
Gravitational potential energy
 All to do with the height of an object – when height of
an object changes, its gravitational potential energy
changes.
Ep = mg h
 Where
Ep is the increase in gravitational potential
energy in joules (J)
 M = mass in kg of the object being lifted
 G = strength of gravity, 10N kg-1
Gravitational potential energy
 All to do with the height of an object – when height of
an object changes, its gravitational potential energy
changes.




Ep = mg h
Where
Ep is the increase in gravitational potential
energy in joules (J)
M = mass in kg of the object being lifted
G = strength of gravity, 10N kg-1
h = change in height, in metres
Example
 A 5kg object is lifted to a height of 2m above the floor
it was resting on.
1. Calculate the gain in gravitational potential energy
on the object.
Example
 A 5kg object is lifted to a height of 2m above the floor
it was resting on.
1. Calculate the gain in gravitational potential energy
on the object.
2. How much gravitational potential energy does the
object lose if it is dropped and falls back down to the
floor?
Example
1 and 2 have the same answer.
Ep = mg h = 5 x 10 x 2 = 100J
Example
1 and 2 have the same answer.
Ep = mg h = 5 x 10 x 2 = 100J
 Object is lifted 2m off the floor. Gain in gravitational
potential energy = 100J (g = always 10) so 10x10
Example
1 and 2 have the same answer.
Ep = mg h = 5 x 10 x 2 = 100J
 Object is lifted 2m off the floor. Gain in gravitational
potential energy = 100J (g = always 10) so 10x10
 The object has 100J more gravitational potential
energy when 2m off the floor
Example
1 and 2 have the same answer.
Ep = mg h = 5 x 10 x 2 = 100J
 Object is lifted 2m off the floor. Gain in gravitational
potential energy = 100J (g = always 10) so 10x10
 The object has 100J more gravitational potential
energy when 2m off the floor
 The object falls 2m. Loss in gravitational potential
energy is 100J
Formula
Ep
10m
h
Question
 Khyati and her mother go up in a lift. Khyati’s mass is
45kg and she gains 5400J of gravitation potential
energy as she goes up in the lift. Calculate the height
Khyati gains.
 Kyhati’s mum gains 7800J GPE. Calculate her mass.
Important use of GPE
 Hydroelectric power – water stored behind a dam has
GPE.
Important use of GPE
 Hydroelectric power – water stored behind a dam has
GPE.
 The water goes through an exit at the top of the dam
and drops to the bottom of the dam
Important use of GPE
 Hydroelectric power – water stored behind a dam has
GPE.
 The water goes through an exit at the top of the dam
and drops to the bottom of the dam
 As the water falls, GPE is changed into kinetic energy
Important use of GPE
 Hydroelectric power – water stored behind a dam has
GPE.
 The water goes through an exit at the top of the dam
and drops to the bottom of the dam
 As the water falls, GPE is changed into kinetic energy
 At the bottom of the dam, the kinetic energy is
changed to electrical energy by the turbines of the
power station.
Questions
Calculate the GPE a boy of mass 75kg gains if he
climbs 50 steps, each step having a height of 20cm
2. A girl, mass 55kg, jumps off a bridge into the water
below. The bridge is 2.5m above the water, Calculate
the GPE the girl lost when she hits the water.
1.