1. ENERGY, WORK & SIMPLE MACHINES

2. the nature of Energy

3. Energy — the ability to cause change Forms of energy include:
Electrical
Chemical
Thermal
Radiant

4. Kinetic Energy — energy in the form of motion KE depends on mass and velocity of moving object. Example of KE: Going down a slide

5. Potential Energy — energy that is stored
Example of PE:
Waiting at top of slide
Elastic Potential Energy – energy stored by something that can stretch or compress, such as rubber band or spring

6. Chemical Potential Energy – energy stored in chemical bonds
A glass of milk has CPE until you drink it then calories are used as energy for your body
Gravitational Potential Energy – anything that can fall has stored GPE
A ball on a ledge has GPE

7. Conservation Of Energy

8. Mechanical Energy — total amount of kinetic energy and potential energy in a system 
Mechanical Energy = PE + KE
POINT A: PE MAXIMUM, KE = O
POINT B: KE , PEx
POINT C: KE , PE
POINT D: PE MAXIMUM, KE = O
: TOTAL MECHANICAL ENERGY
SWING

9. The Law of Conservation of Energy – energy may change form but it cannot be created or destroyed under ordinary conditions.
No energy is lost, just friction converts mechanical energy into thermal energy
The breakfast you eat converts chemical energy into mechanical energy, heat energy so your muscles can help you pump your legs.
Air resistance converts mechanical energy into thermal energy

10. Work

11. Work — transfer of energy that occurs when a force makes an object move
For work to be done, something has to move and the motion must be same direction as force.
When work is done, a transfer of energy always occurs.

12. Calculating Work Ex. You push a wheelbarrow with a force of 100N
Calculating Work Ex. You push a wheelbarrow with a force of 100N. You moved the wheelbarrow 5m. How much work did you do?
Work (joules) = Force (Newtons) x Distance (meters)
W = F x d
W = F x d
W = (100N) x (5m)
W = 500 J

13. Power (watts) = work(J) P = W
Power – the rate at which work is done. Ex. You do 900 J of work pushing a fridge. I t took 5 seconds. What was your power?
Calculating Power
Power (watts) = work(J) P = W
time (s) t
P = W = 900J = 180J/s = 180 watts (w)
t s

14. Using Machines

15. Machine — device that makes doing work easier Machines make work easier by increasing the force that can be applied to an object.

16. Two forces are involved when machine does work
(FIN) Input Force
The Force applied
to machine
Output Force (FOUT)
The force applied by machine
Output Force
Input Force

17. Machines can be made more efficient by reducing friction.
Mechanical advantage – the ratio of the output force to the input force
Efficiency – measure of how much work put into a machine is changed into useful output work by the machine.
Machines can be made more efficient by reducing friction.
Mechanical advantage = output force (newtons)
Input force (newtons)
MA = FouT
FIN

18. Simple Machines

19. Simple Machine — machine that does work with only one movement of the machine
LEVER
PULLEY
Bar that is free to pivot
around fixed point (fulcrum)
1st Class Lever – fulcrum is between the input force and output force
2nd Class Lever – output force is between fulcrum and input force
3rd Class Lever – input force is between fulcrum and output force
Grooved wheel with a rope, chain or cable running along groove
Fixed pulley – attached to something that doesn’t move
Moveable pulleys – one end of the rope is fixed and the wheel is free to move
Block and Tackle – system of pulleys consisting of fixed and moveable pulley

20. WHEEL AND AXLE
Consists of an axle attached to center of a larger wheel so that the wheel and axle rotate together
INCLINED PLANE
Sloping surface, such as a ramp that reduces the amount of force required to do work
THE SCREW
Inclined plane wrapped in a spiral around a cylindrical post
THE WEDGE
An inclined plane with one or two sloping sides