1. Thursday, March 9
____________ is the force of two objects pressing together.
2. Friction produces _____________.
3. The more force gravity pulls down on an object, the ________ friction there will be.
4. We can reduce friction by making surfaces more ___________________.
5. We can increase friction by making surfaces more __________________.

2. Work, Power & Simple Machines

3. Two physics students, Ben and Bonnie, are in the weightlifting room.
Bonnie lifts the 50 kg barbell over her head (approximately .60 m) 10 times in one minute;
Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds.
Which student does the most work?
Which student delivers the most power?
Explain your answers.

4. A force is a push or a pull. Energy is the ability to do work
A force is a push or a pull. Energy is the ability to do work. Work is using a force to move an object.

5. Work: using force to move something
Formula for work:
W=f X d
Work is measured in Joules (J). James Prescott Joule  (1818 – 1889) was an English physicist

6. Power is the amount of work done in a certain amount of time.
Formula= Joules per second=watt (James Watt steam engine)=horsepower

7. Two physics students, Ben and Bonnie, are in the weightlifting room.
Bonnie lifts the 50 kg barbell over her head (approximately .60 m) 10 times in one minute;
Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds.
Which student does the most work?
Which student delivers the most power?
Explain your answers.

8. Machines made work easier.

9. History of Work
Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.

10. Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work easier.

11. What do machines do? Change the direction of a force.
Increase the strength of a force.
Increase the distance of a force.
Increase the speed of a force.

12. 6 Types of Simple Machines
1. Lever

14. 6 Types of Simple Machines
2. Wheel and axle

15. 6 Types of Simple Machines
3. Pulley

16. 6 Types of Simple Machines
4. Inclined Plane

17. 6 Types of Simple Machines
5. Wedge
Cuts or splits objects. Has a slanted or sharp edge.

18. 6 Types of Simple Machines
6. Screw
Inclined plane wrapped around a pole to hold things together or lift things.