1. Net force, F=ma, and friction
Forces and Friction
Net force, F=ma, and friction

2. Balanced Forces:

5. Unbalanced Forces: push the book!

7. Reminder: Newton’s 2nd Law:
The force on an object is directly proportional to the object’s mass and acceleration:
F = ma
For gravity, acceleration = g near the Earth’s surface so
F = mg or W=mg (Weight)

8. Force = mass x acceleration

9. How to find the net force on an object:

10. Determining net force in linear directions:

11. Remember: Newton’s 1st Law still applies:

12. Free fall: Elephant and peanut
With air resistance, the peanut takes much longer to fall.

13. Elephant and peanut: without air resistance
Without air resistance, the acceleration due to gravity is the same so they fall at the same rate. However, the force of impact varies because one has more mass than the other one.

14. Air resistance and terminal velocity:
When the force due to air (or any fluid) reaches a point equal to the gravitational force, then the object will no longer accelerate and has reached terminal velocity.

15. Terminal Velocity: Gravity balances air resistance force

16. Friction: force that opposes motion

17. Friction misconception:
Friction depends on the type (composition) of the two surfaces and the amount of contact the molecules of each surface have with each other. If you push the surfaces together more, you increase the amount of contact, thus increasing friction.

18. Static vs. Kinetic Friction:

19. Balanced or Unbalanced
Balanced or Unbalanced?: Draw a force diagram to show forces on these objects 1. 2. 5. 3. 4.
If unbalanced, what is the cause? (air resistance, friction, etc.)

20. Describe the following with respect to Newton’s 1st and 2nd Laws of motion: