1. Foundations of Science
Motion & Force
Foundations of Science

2. Objectives
Explain the effects of unbalanced forces on the motion of objects
Compare and contrast static and kinetic friction
Describe how friction may be either harmful or helpful
Identify ways in which friction can be reduced or increased

3. Force
Force: an action exerted on a body in order to change the body’s state of rest or motion
Usually many forces acting on an object at any given time
Net Force: combination of forces acting on an object
Object moves/accelerates in the direction of the net force

4. Balanced Forces
When forces applied to an object are equal, then the forces are balanced
This means that the object does not change its motion

5. Unbalanced Forces
If the net force is greater than zero, then the object will move in the direction of the greater force

6. Forces Not Directly Opposite
If the forces are not directly opposite each other
Moving a box:
Person 1: Pushes North
Person 2: Pushes East
What direction is the box moving?

7. Friction
Friction is due to the fact that the surface of objects are rough
Small hills and valleys that cause one surface to stick to another

8. Friction Moving Objects: Car moving at a constant speed
As long as force applied and friction/air resistance stay the same the car will continue moving at the same pace
Stationary Objects:
Parked Car
Friction of tires opposes the pull of gravity against the car, keeping it from moving (parking brake?)

9. Types of Friction
Static Friction: friction between 2 stationary surfaces
Kinetic Friction: Friction between 2 moving surfaces
Sliding friction: objects slide past each other
Rolling friction: objects rolls over a flat surface
Static Friction > Kinetic Friction
Sliding Friction > Rolling Friction

10. Types of Friction

11. Sliding Friction
Is it easier to slide a down a slide wearing pants, or shorts?

12. Rolling Friction

13. Other Types of Friction

14. Friction: Good, Bad, & Inbetween
Good: Friction allows a car to move, or skis to whoosh you down a mountain
Bad: Friction in a car’s motor can cause serious wear and tear on the motor, leading to the need to replace parts at regular intervals
In-between: Adding salt to roads increases friction, which keeps cars from sliding Or
Adding lubricants, like motor oil, decreases the friction in an engine, protecting its moving parts from the harmful effects of friction

15. Moving A Car