1. (Types of forces part 1)

2. A force is a push or pull, or any action that has the ability to change motion.

3. The force of gravity on an object is called weight. Mass and weight are not the same thing! (Mass = how much stuff) (Weight = the force of gravity pulling on that stuff)

4. A 10-kilogram rock has a mass of 10 kilograms no matter where it is in the universe. A 10-kilogram rock’s weight however, can vary greatly depending on where it is. Weight

6. Bigger objects have a stronger gravitational force Closer objects have a stronger gravitational force

7. Many kinds of friction exist.

8. 1. Type of surface 2. Amount of force

9. Friction depends on both of the surfaces in contact. Surface Matters! Just read: (When the hockey puck slides on ice, a thin layer of water between the rubber and the ice allows the puck to slide easily.)

10. The greater the force squeezing two surfaces together, the greater the friction force. Try it with your hands

11. Friction is a force, measured in newtons just like any other force. Static friction keeps an object at rest from moving.

12. Sliding friction is a force that resists the motion of an object moving across a surface.

13. Other types of friction

14. Friction is also important to anyone driving a car. Grooved tire treads allow space for water to be channeled away from the road-tire contact point, allowing for more friction in wet conditions.

15. Shoes are designed to increase the friction between their soles and the ground.  Players wearing cleats can apply greater force against the ground to help them move and to keep from slipping. Why do you think these shoes increase friction?

16. Can you think of examples where friction is not so helpful? When you….. –Skin your knee……. falling  –Hit a rock on your skateboard…. and fall  –Trip…… and fall  –Run into a glass door… and fall  –Trying to run over ice….. And fall 