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# Friction

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Friction

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### Friction

1. 1. FRICTION
2. 2. A force that opposes motion
3. 3. Objectives… <ul><li>Explain why friction occurs. </li></ul><ul><li>List the two types of friction, and give examples of each type. </li></ul><ul><li>Explain how friction can be both harmful and helpful. </li></ul>
4. 4. What is friction? <ul><li>Is a force that opposes motion between two surfaces that are in contact </li></ul>
5. 6. When does friction occur? <ul><li>Friction occurs when two surfaces are in contact </li></ul>
6. 7. Also… <ul><li>When a liquid or gas is pushed out of the way of a moving object </li></ul>
7. 8. Why does friction occur? <ul><li>Because the hills and valleys of a surface are in contact with the hills and valleys of other surfaces, this produce friction. </li></ul>
8. 10. Friction depends on… <ul><li>Roughness of surfaces and </li></ul><ul><li>Force that objects are being pressed one against the other; or their weights </li></ul>
9. 11. What increases friction? <ul><li>Rough surfaces </li></ul><ul><li>And weight of objects </li></ul>
10. 12. What does the amount of surfaces depend on? <ul><li>the amount of friction depends on how well the surfaces grip each other. Tyres on a road have very high friction (they don't slip), skates on ice have very low friction (they slip easily). </li></ul>
11. 13. In a liquid or a gas <ul><li>For a solid object moving through a liquid or gas, the amount of friction depends on the shape and surface area of the object and the viscosity (thickness or thinness) of the liquid. </li></ul>
12. 14. TYPES OF FRICTION <ul><li>KINETIC AND </li></ul><ul><li>STATIC </li></ul>
13. 15. What is kinetic friction? <ul><li>Is the friction between two moving surfaces </li></ul>
14. 16. Sliding and Rolling
15. 17. Static friction <ul><li>It occurs when a force is applied to an object but this object doesn’t move. </li></ul>
16. 18. Static friction
17. 19. Is friction good or bad? <ul><li>Friction can be good. When we walk we push backwards against the ground, the opposing force pushes us forwards. Without friction our feet would slip and walking would be impossible. </li></ul>
18. 20. It is also good <ul><li>To stop your bicycle (brake system) </li></ul>
19. 21. But sometimes is bad… <ul><li>Soil erosion caused by wind (friction of a fluid). </li></ul><ul><li>Holes in your shoes, jeans. (friction of a solid) high friction </li></ul><ul><li>Lack of friction is dangerous too, you may fall if the floor is very slippy. </li></ul>
20. 22. Some ways to reduce friction
21. 23. Some ways to increase friction