1. Physics CP

2. What is work? We do work when we lift a load against gravity. The heavier the load or the higher we lift it, the more work we do.

3. What is work? Two factors: The application of a force. The movement of something by that force. In the most simple case (a constant force and that force being applied in a straight line)… Work = Force x Displacement Or W = Fd

4. What is work? - Definition  Work is done on an object when a force causes a displacement of the object  Work done by a constant net force is: W net = F net d WRITE THIS DOWN!

5. What is work? – Key Concepts  Work is not done on an object unless the object is moved with the action of a force.  The application of a force does not constitute work.  Work is done only when components of a force are parallel to a displacement.  When the force of an object and the object’s displacement are in different directions, only the component of force that is parallel to the object’s displacement does work.  Components of force that are perpendicular to a displacement do not do work.

6. What is work? – For Example Compared to a single load that we lift one story… If we lift two loads up one story, we do twice as much work. The force needed to lift twice the mass is twice as great. If we lift one load two stories instead of one story, we also do twice as much work because the distance is twice as great.

7. Two Categories of Work Work done against another force: Push-ups An archer pulling a bowstring Work done to change the speed of an object: Throwing a baseball Speeding up or slowing down a car

8. Measurement of Work The unit for work is called the joule (rhymes with “cool”) One joule of work is done when a force of 1 Newton is exerted over a distance of 1 meter. A weight-lifter typically does work in the order of thousands of joules. It takes millions of joules to bring a truck traveling at 60 miles per hour to rest.

9. Energy Energy is the “something” that allows us to do work; the capacity of a system to do work. As energy allows work, it is also measured in joules. Energy Types - (as far as we’re concerned) Kinetic (Mechanical) Potential (Stored) Heat

10. Energy – The Full List Mechanical Energy Kinetic Elastic Potential Surface (surface tension) Sound Gravitational Energy Thermal Energy

11. Energy – The Full List Electric Energy Electrostatic Electricity Magnetic Electromagnetic Chemical Nuclear

12. Energy - Examples Nanojoule (one billionth) – 1/160 th the kinetic energy of a flying mosquito. Microjoule (one millionth) – energy produced by a collision in the LHC. Kilojoule (one thousand) – about the amount of solar radiation received by one square meter of the Earth in one second. Megajoule (one million) – kinetic energy of a one ton vehicle moving at 100 mph. Gigajoule (one billion) – 6 gigajoules of chemical energy contained in a barrel of oil. Terajoule (one trillion) – about 60 terajoules were released by the atomic bomb detonated over Hiroshima.

13. Conservation of Energy Energy is neither created nor destroyed. It is only transferred from one form to another.

14. Kinetic Energy Work required to accelerate a mass to a given velocity. Derivation…

15. Potential Energy (Gravitational) The potential energy gravity provides before an object falls. Derivation…

16. Power Power is defined as work done over time, or… P = W/t The unit of power is the watt (W). One horsepower is approximately 0.75 kW – so a 134 horsepower engine has about 100 kW of power. This is the same amount of power (effectively) required to light one thousand 100 watt light bulbs.

17. Power - example An old forklift is replaced with a new one that has twice the power… Compared to the old forklift, how much more of a load can the new one lift in the same amount of time? How much time will it take to lift the same load?