1. Force & Motion Part 2 Mrs. Wright

2. LET’S REVIEW… Force: A push of pull applied to an object Friction: The force that one surface exerts on another when the two surfaces rub against each other.

3. FRICTION Friction is caused by microscopic bumps on surfaces called: MICROWELDS The picture on the right is of Aluminum Foil at 10,000X magnification.

4. Friction Is Very Useful… Friction keeps our feet from sliding out from under us when we are walking Friction keeps our shoelaces tied Friction gives us the ability to open a round door knob. Can you think of others things it would be hard to do without friction?

5. FRICTION Depends On 3 Things How hard the surfaces push together The surface areas in contact with each other Types of surfaces involved Example of Friction Sled moving across the snow The bottom of the sled rubs against the snow Fireman sliding down the pole The skin of his hands rub against the polished metal

6. 4 Types of Friction Static Friction The friction that acts on objects that are not moving Initial friction when moving an object Example

7. 4 Types of Friction Sliding Friction Occurs when two solid surfaces slider over each other. Example

8. 4 Types of Friction Sliding Friction Occurs when two solid surfaces slider over each other. Example

9. Rolling Friction When an object rolls across a surface

10. 4 Types of Friction Fluid Friction Occurs when a solid object moves through a fluid Fluid – a material that FLOWS Water Oil AIR Example

11. How well were you listening? STAND UP…

12. What are the four types of friction?

13. Can you show me an example of sliding friction?

14. Give me a new example of rolling friction.

15. Give me a new example of fluid friction

16. Another Type of Force… GRAVITY A force that PULLS objects toward each other People all around the planet are being pulled toward the surface of the Earth. Gravity pulls everything toward the Earth’s surface at a rate of 9.8m/s 2

17. WEIGHT VS. MASS Mass: the measure of the amount of matter in an object, measured in grams on a balance Weight: A measure of the gravitational force exerted on an object BECAUSE of its mass WEIGHT = Mass (kg) X Gravity (9.8m/s 2 ) 100kg X 9.8m/s 2 100kg X 9.8m/s 2 WEIGHT = 980N

18. WEIGHT VS. MASS

19. FORCES The strength of a force is measured in the SI unit called the NEWTON (N). You exert about 1N of force when you lift a small lemon The direction AND strength of a force can be represented by an arrow. The arrow points in the direction of the force. The length of the arrow tells you the strength of the force – the longer the arrow, the greater the force.

20. FORCES NET FORCES The combination of ALL forces acting on an object The net force determines whether An object moves & what direction it moves in

21. Combining Forces When forces act in the same direction, the net force can be found by ADDING the strengths of the individual forces

22. Combining Forces When forces act in opposite directions, they also combine to produce a net force, HOWEVER, you must pay attention to the direction of the each force. When two forces act in opposite directions, they combine by SUBTRACTION

23. UNBALANCED FORCES Unbalanced forces can cause an object to start moving, stop moving, OR change direction. Unbalanced forces acting on an object result in a net force and cause a change in the object’s direction Tug of War

24. Balanced Forces Equal forces acting on one object in opposite directions are called balanced forces Balanced forces acting on an object DO NOT change the object’s motion

25. Time To Stand Up Again…

26. Explain Unbalanced Forces

27. Give a new example of an unbalanced force

28. Explain Balanced Forces

29. Give a new example of a balanced force