1. Motion and Force

2. What is force? Any action that can change the state of motion of an object. Has a magnitude and direction

3. Fundamental forces

4. Vary in strength. –SN is strongest, holds nuclei of atoms together, effective over a very short distance –EM force is about 1/100 of the SN force –Gravitational force is much weaker. Can act through contact or at a distance. –Contact  push, pull –Field  gravity, magnetic

5. Balanced vs Unbalanced Forces Net force – combination of all the forces acting on an object *When there is a net force acting upon an object, the object accelerates in the direction of the net force. - No acceleration occurs if net force is 0!

6. Balanced forces (no net force) do not change motion. Unbalanced forces (net force > 0) do not cancel completely, objects will accelerate in the direction of the greater force. Think of tug-of-war!

7. Friction Force that opposes motion between two surfaces that are in contact. Occurs because the surfaces of objects are not perfectly smooth.

8. Types of Friction Static friction  resists the initiation of sliding motion between two surfaces that are in contact and at rest. Kinetic friction  opposes the movement of two surfaces that are in contact and are moving over each other.

10. Static friction is greater than kinetic friction. Different types of kinetic friction – sliding, rolling, fluid, etc.

11. Friction and Motion Friction is necessary for many everyday tasks! –Think of your typical day! Tires push against ground to make your car move. Brakes use friction to stop your car. Friction between hands & steering wheel. Friction between pencil and paper allows you to write. Friction between your feet and floor allow you to push off when you walk.

12. Check for understanding... 1.Describe a situation in which unbalanced forces are acting on an object. How is it affected? 2.Identify the type of friction. a.Two students push a box that is at rest. b.Box pushed by students is now sliding. c.Students put rollers under box and push it forward.

13. Newtons? Force is measured in N. –Newton is the force required to cause a mass of 1kg to accelerate 1 m/s/s Force is calculated using: F = ma –Force is equal to mass x acceleration.