1. Chapter 2: Forces

2. - All forces have size and direction
What is a Force?
- a push or a pull
- All forces have size and direction
- Forces can change the acceleration of an object
Examples: Gravity and magnetism

4. Unit used for force: - Forces are expressed in newtons (N)
- Named after English Scientist Sir Isaac Newton
- Example: You exert about one newton of force to lift a small apple.

5. Net force: - the combination of all the forces acting on an object
Depends on:
- Direction of the forces

6. Calculating Net force Subtract the forces Add the forces together
Forces in opposite directions:
Subtract the forces
The direction will be the same as the larger force
Forces in the same direction:
Add the forces together

9. Let’s practice some net force equations.

10. 2) will not cause a change in the motion of an object
Balanced Forces
1) produce a net force of 0 N
2) will not cause a change in the motion of an object

12. 1) net force acting on an object does not equal 0 N
Unbalanced Forces
1) net force acting on an object does not equal 0 N
2) produce a change in motion – either speed or direction.
3) motion cannot continue without unbalanced forces acting on the object.

14. 6N, right

18. Chapter 2: Forces
Friction and Gravity

19. Friction
Friction – a force that opposes motion between two surfaces that are in contact. - cause a moving object to slow down and eventually stop What would happen to the motion of the moving object if there was no friction? It would continue to move in the same direction at the same rate of speed.

20. The Source of Friction
There is friction between any two surfaces that are in contact.
The amount of friction depends on many factors, including:
1) the force pushing the surfaces together
2) the roughness of the surfaces.

22. Force and Friction
- If the force pushing two surfaces increases, friction increases. Therefore, objects that weigh more exert more force and experience more friction.

23. Surface Texture and Friction
The rougher the surface, the greater the friction.
Ex. a ball rolling on the ground vs. a puck sliding on ice

24. Types of Friction
kinetic friction Kinetic friction is friction between moving objects. There are three types: 1) sliding 2) rolling 3) fluid - sliding produces the most friction and fluid produces the least.
Static Friction
a force is applied to an object but the object does not move
- net force is 0 N and the object remains stationary

26. Sliding Friction
Rolling Friction

27. Fluid Friction

29. Harmful and Helpful Friction
Friction is necessary for every activity you do like:
- writing on paper
- sitting in your chair
walking (or running) to your classes
Friction is also responsible for:
- the wear on car engine parts
- erosion
- skinned knees when you fall
Sometimes it is necessary to increase or decrease friction.

30. Reducing Friction
Lubricants – reduce friction by changing sliding friction into fluid friction Examples of lubricants are oil, grease, or wax. Other ways to reduce friction are: - by changing sliding friction to rolling - or by making the surfaces that are in contact smoother

31. Increasing Friction
- occurs when the surfaces are made rougher. Ex. sand on icy roads - Increasing force will also increase friction