MOVEMENT AND CHANGE

1
MOVEMENT AND CHANGE

• Forms of energy
• Gravitational potential energy

2
FORMS OF ENERGY

• There are several forms of energy.
• Thermal energy
• Caused by the movement energy of molecules.

3
FORMS OF ENERGY

• Kinetic energy (KE)
• This is the energy all moving objects have.
• A moving lorry has lots of kinetic energy!

4
FORMS OF ENERGY

• Chemical energy
• Energy which is stored in food or fuels

5
FORMS OF ENERGY

• Sound and light energy
• Common types of energy

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FORMS OF ENERGY

• Electrical energy
• Very common and useful
• (Magnetic energy is always connected with
  electrical energy)

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FORMS OF ENERGY

• Nuclear energy
• Energy stored in the centre of the atom

8
FORMS OF ENERGY

• Gravitational potential energy
• When an object is moved to a higher place it
  gains stored energy which it can give out if it
  falls down.

9
The Principle of Conservation of Energy

• Energy can be changed from one form to another
  but it cannot be created or destroyed.

10
Falling under gravity

• A diver may use 6000J of energy climbing to the
  top of a board.
• At the top of the board he has 6000 J of
  gravitational potential energy (PE) but no
  kinetic energy (KE).
• As he dives, his PE is converted into an equal
  amount of KE

11
Falling under gravity

• The total amount of PE KE is always 6000J!

12
The Pendulum
13
The Pendulum

• When a pendulum swings to and fro, its energy is
  constantly changing from potential energy (PE) to
  kinetic energy (KE) and back again.

14
The Pendulum

• The energy eventually is converted to heat by
  friction with the air.
• This heat is low grade energy and we can not
  make use of it
• All energy eventually becomes low grade.

15
Calculating Potential Energy

• For a weight lifter lifting a mass of 200 kg up
  a height of 2 m we can work out the gain in
  potential energy.
• Potential energy work done weight x height
  lifted

16
Calculating Potential Energy

• On Earth
• weight (in N)
• mass (in kg) X 10 so
• PE mass x 10 x height

17
Calculating Potential Energy

• Gravitational PE mass x g x height
• (in joules) (kg) (N/kg)
  (m)
• On Earth g 10, but g has different values on
  other planets