1. Momentum Defined Easier to stop a compact car than a Greyhound bus
Bus has more MOMENTUM
Momentum = mass X velocity
Momentum = mv

2. Impulse Defined Forces change motion, so velocity changes
If velocity changes, momentum changes
Amount of momentum change depends on how long we apply the force
Impulse = force X time

3. Impulse and Momentum Related

5. Conservation of Momentum
“In the absence of an external force, the momentum of a system remains unchanged.”
When a quantity doesn’t change, we say it is conserved
Very deep meaning, connected with the idea that the Laws of Physics are unchanged if you move to a new location

6. Elastic Collisions

7. Inelastic Collisions

8. Energy According to Einstein, a counterpart to mass
An enormously important but abstract concept
Energy can be stored (coal, oil, a watch spring)
Energy is something moving objects have
How to deal with this idea???

10. Work Easiest to start with the notion of work Work = Force X Distance
To lift a box from the floor, you apply a force to overcome gravity
Multiply that force by the distance through which you apply the force and you calculate the amount of work accomplished

11. Is this Work?

12. Work
Unit is the JOULE
A Joule is a newton-meter

13. Power The rate at which work is done
Takes more power to run up the stairs than to walk up the stairs, but the energy consumed is the same in either case

14. Power Unit is the WATT A Watt is a newton-meter per second
Think of 100-Watt light bulb
Bigger units are kilowatts and megawatts
Utility sells energy in kilowatt-hours
1 KWh = 1000 Joules/second times 3600 Seconds = 3.6 X 106 Joule

15. Potential Energy
If we lift an object from the floor into the air, it has the potential to do work for us
This ability to do work is called POTENTIAL ENERGY
Other forms of potential energy include the compression of a spring, the stored energy in coal or oil, the stored energy in a uranium nucleus

16. Potential Energy Gravitational potential energy is simple to calculate
Gravitational Potential Energy = weight X height

17. Gravitational Potential Energy
Independent of Path to get there

18. Kinetic Energy The energy of moving objects
Kinetic Energy = 1/2 Mass X Speed2

19. Energy Conversion

20. Energy Conversion

21. Work-Energy Theorem
Work done on an object can give the object either potential or kinetic energy or both
If we do work on an object to lift it into the air, we give it potential energy
If we do work on an object and set it into motion, we give it kinetic energy
The work-energy theorem relates to the second case

22. Work-Energy Theorem
If we do work on an object and set it into motion without changing the object’s potential energy, the work done appears as kinetic energy of the object

23. Conservation of Energy
Perhaps the most important discovery of the past two centuries
In the absence of external work input or output, the energy of a system remains unchanged. Energy cannot be created or destroyed.
Remember from Einstein, that mass is a form of energy

25. Collisions
Elastic Collisions conserve both momentum and kinetic energy
Inelastic Collisions conserve momentum by energy is lost to heat

26. Machines
A device that multiplies forces by taking advantage of the definition or work and the conservation of energy
Work input = Work output
Levers

27. Machines

28. Machines

29. Efficiency
In many machines, some energy is lost due to friction. This may be metal-on-metal (oil the parts to reduce friction) or air resistance (energy loss moves molecules in the air faster giving them kinetic energy).

30. Energy Sources
For the earth, there are two energy sources, the sun and radioactive decay in the earth’s interior
The earth receives about 1400 Joules/meter2 each second
This is 1.4 kW per square meter
Recover for use in plants (burn wood)
Recover from wind

31. Man’s Need for Power Man can generate about 75 Watts to do work
Domesticated Animal about 750 Watts
Machines limited by size
Power plants generate electricity in the hundreds of megawatt range