1. Energy and Machines
Physical Science

2. What is Energy? Is the ability to do work Two general types
Kinetic Energy
Potential Energy

3. Kinetic Energy The energy of motion Depends on mass and speed
Measured in Joules (J)
Symbol = KE

4. Potential Energy Energy that is stored (not moving)
Based on position and height
Measured in Joules (J)
Symbol = PE

5. Is it Kinetic or Potential Energy?
Rock sitting on the cliff’s edge
A car going down a hill
Sitting at the top of a slide
Going down a slide

6. Calculating Kinetic Energy
Example Problem The cart on a roller coaster has a mass of 100 kg. It is going a speed of 6 m/s along the track. How much kinetic energy does it have?
Formula
KE = ½ m * v2
KE= kinetic energy (J)
m= mass (kg)
v= velocity (m/s)

7. Calculating Potential Energy
Example Problems A 30 kg rock is sitting on a ledge 5 m from the ground of Earth. How much potential energy does it have?
Formula
PE = m * g* h
PE = potential energy (J)
m= mass (kg)
g= gravity (9.8)
h= height (m)

8. How to also write PE formula
PE = m*g*h
Weight
PE= Fgh

9. Forms of Energy Thermal Energy Mechanical Energy
Motion and Position of everyday objects
Examples
Speeding trains
Bouncing balls
Thermal Energy
Total PE and KE of the particles in an object
Examples
Liquid metals

10. Forms of Energy Chemical Energy Electrical Energy
Energy stored in chemical bonds
Examples
Chemical reactions
Burning coal
Electrical Energy
Energy associated with electric charges
Examples
CD players
Calculators

11. Forms of Energy Nuclear Energy Electromagnetic Energy
Form of energy that travels through space in the form of waves
Examples
X-rays
Visible Light
Nuclear Energy
Energy in atomic nuclei
Examples
Sun
Nuclear power plants

12. Energy Conversion Energy changing from one form to another Examples
Kinetic to Potential
Mechanical to Thermal

13. Law of Conservation of Energy
States:
Energy cannot be created nor destroyed, only changed
Meaning
Amount of energy at the start must equal amount of energy at the end

14. Energy Conversion: Roller Coaster
PE Greatest
Conversion
PE decrease
KE increase
PE = KE
KE Greatest
KE decrease
PE increase
KE = PE

15. Energy Conversion: Pendulum
PE Greatest
Conversion
PE decrease
KE increase
PE = KE
KE Greatest
KE decrease
PE increase
KE = PE

16. Energy Conversion: Throwing Ball Up
KE Greatest
Conversion
PE increase
KE decrease
PE = KE
PE Greatest
PE decrease
KE increase
KE = PE

17. Machines

18. What is a Machine? A device that makes doing work easier Two divisions
Simple machines
Compound Machines

19. How do Machines make work Easier?
Increase Force
(ex: car jacks)
Increase the distance a force is applied
(ex: using a ramp)
Changing the direction of an applied force
(ex: ax blade)

20. Simple Machines
Machines that does work with only one movement of the machine

21. Six types of Simple Machines
1). Lever
A bar that is free to pivot or turn around a fixed point (ex: teeter totter)
2). Pulley
Grooved wheel with a rope, chain, or cable running along the groove (ex: wishing well)

22. Six types of Simple Machines
3). Wheel & Axle
A shaft/axle attached to the center of a larger wheel so that both rotate together (ex: door knobs)
4). Inclined Plane A sloping surface (ex: ramp)

23. Six types of Simple Machines
5). Screw
An inclined plane wrapped in a spiral around a cylindrical post (ex: jar lids)
6). Wedge
An inclined plane with one or two sloping sides (ex: knife)

24. What are Compound Machines?
When two or more simple machines operate together
Example: Can Opener
Wheel & Axel
Level
Wedge

25. Input force & Output force
Force applied TO the machine
Symbol = Fin
Output Force
Force applied BY the machine
Symbol = Fout

26. Input Work & Output Work
Work done by you on a machine
Symbol = Win
Output Work
Work done by the machine
Symbol = Wout

27. Input & Output Work: The Relationship
Input work equals Output work in an ideal machines
Win = Wout
Why?
Law of conservation of Energy
Energy is not created nor destroyed

28. What is Mechanical Advantage?
Is the number of times that a machine increases an input force
Two Versions
Actual Mechanical Advantage (AMA)
Ideal Mechanical Advantage (IMA)

29. Actual Mechanical Advantage
Determined by measuring the actual forces on a machines
Ratio of the output force to the input force

30. Actual Mechanical Advantage Formula
AMA = Fr / Fe (Big/Small)
AMA= actual mechanical advantage
Fr= resistance force (output force)
Fe=effort force (input force)
AMA has no unit
Fr & Fe has the unit of “N”

31. AMA Formula Practice
1) What is the actual mechanical advantage of a machine who’s input force is 30-N but produces an output force of 90-N?
2) You test a machine and find that it exerts a force of 10 N for each 2 N of force you exert operating the machine. What is the actual mechanical advantage of the machine?

32. Ideal Mechanical Advantage
Is the mechanical advantage in the absence of friction
Because friction is always present, the actual mechanical advantage of a machine is always less than the Ideal

33. Ideal Mechanical Advantage Formula
IMA = de / dr (Big/Small)
IMA = ideal mechanical advantage
de = displacement of effort force (input distance)
dr = displacement of resistant force (output distance)
IMA has no unit
de and dr has the unit of meters

34. IMA Formula Practice
1) A woman drives a car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the IMA?
2) A construction worker moves a crowbar through a distance of 4 meters to lift a load 0.5 meter off the ground. What is the IMA of the crowbar?

35. What is efficiency? %
The percentage of work input that becomes work output
Because there is always some friction, the efficiency of any machine is always less than 100 percent

36. Efficiency Formula Wout = work output (J) Win = work input (J)
Small/Big x 100

37. Efficiency Formula Practice
1) You have just designed a machine that used 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine?