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# Unit 20 - Forces And Friction

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Forces and Friction

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### Unit 20 - Forces And Friction

1. 1. Forces<br />
2. 2. Types of Forces<br />Thrust<br />Lift and Drag<br />Magnetism<br />Push<br />Pull<br />Gravity<br />
3. 3. What Forces Do<br />If forces are unbalanced the object will do one of the following things:<br /><ul><li>Begin to move
4. 4. Stop moving
5. 5. Change direction</li></li></ul><li><ul><li>Speed up
6. 6. Slow down
7. 7. Change shape</li></li></ul><li>Balanced Forces<br />The pulling force is equal on both sides, <br />resulting on the rope remaining stationary<br />
8. 8. Balanced Forces<br />Each sumo wrestler is applying equal pushing force, <br />resulting in them remaining stationary<br />
9. 9. Balanced Forces<br />The downward for of gravity is equal to the lifting force of the air under the wings, resulting in the aircraft remaining aloft<br />
10. 10. Balanced Forces<br />The ship is floating on the water, the forces are balanced. <br />Gravity is pulling the ship downward, but the water is forcing the ship upwards due to its displacement of lesser density<br />
11. 11. Equal and Opposite Forces<br />If substances are sufficiently strong, they can not be moved when forces are applied, because they will act in an equal and opposite manner<br />
12. 12. Equal and Opposite Forces<br />In the case of the balancing rocks, the upward force of the lower rocks make up for the downward force of gravity<br />While the balloon pulls upward, the child’s hand pulls downward<br />
13. 13. Equal and Opposite Forces<br />In addition, the forces being applied by gravity can overcome upward forces, with sometimes unfortunate results<br />
14. 14. Equal and Opposite Forces<br />If substances are sufficiently strong, they can not be moved when forces are applied, because they will act in an equal and opposite manner<br />
15. 15. Unequal Forces<br />Those unequal forces will cause movement whether it is horizontal or vertical<br />
16. 16. Unequal Forces<br />If upward thrust or lift exceeds the force of gravity, <br />the spaceship or aircraft will take off.<br />
17. 17. Unequal Forces <br />Drag<br />In sky diving, initially gravity far exceeds drag, and thus you free fall very rapidly (over 100 mph).<br />Once the chute is released, the amount of drag increases dramatically and you slow to under 10 mph<br />
18. 18. Unequal Forces <br />Using drag and lift, wingsuit flyers and paragliders can control where they go and soar around for long periods before eventually landing.<br />
19. 19. Unbalanced Forces<br />The magnetic attractive force is pulling the metal upwards<br />The magnetic force is greater than the force of gravity therefore the metal can be lifted up<br />Gravity is pulling the metal to the ground<br />
20. 20. Unbalanced Forces<br />The magnetic repulsive force is pushing the train upwards<br />The magnetic force is greater than the force of gravity therefore the train can be levitated<br />Maglev technology has potential, because the train is not physically in contact with the track. It hovers and thus there is no friction<br />Gravity is pulling the metal to the ground<br />
21. 21. Balanced and Unbalanced Forces<br />The rubber band is exerting an opposite force to the person pulling on it. <br />It will remain in this state until one of two things happen:<br />The material snaps (pulling force exceeds material strength)<br />Person releases force and rubber band rebounds and launches<br />
22. 22. FRICTION<br />Friction occurs when two substances are in contact with each other<br />The greater the friction, the more force must be applied to move<br />24 mph<br />35 mph<br />5 mph<br />
23. 23. What is friction?<br />Friction is a force that acts when two objects rub together.<br />When the two objects appear to be smooth, there is less friction.<br />When the two objects are rough, there is a greater amount of friction.<br />
24. 24. Friction<br />Road bikes have tiny thin wheels to reduce contact with the ground and friction. In addition, the bikers wear tight fitting clothing to reduce air friction.<br />Mountain bikes have thicker tires to increase contact with the ground, using friction to prevent the biker from slipping and falling in rough terrain.<br />
25. 25. “Friction-less Movement”<br />Some things can be done to reduce friction.<br />Using lubrication such as water or oil can reduce the contact between solid surfaces<br />Air hockey uses air to lift the puck up and allow it to travel rapidly.<br />
26. 26. Friction at the Microscopic Level<br />Even though some objects look smooth, microscopically they are very rough & jagged.<br />As they slide against each other they grind and drag against each other.<br />Flies use microscopic hairs on their feet to grip these jagged edges on the surfaces<br />
27. 27. Different types of Friction:<br />Static Friction: Objects not moving.<br />
28. 28. Different types of Friction:<br />Rolling Friction: Round objects rolling.<br />
29. 29. Different types of Friction:<br />Sliding Friction: Objects moving.<br />
30. 30. Different types of Friction:<br />Fluid Friction: Force through fluids or air.<br /> When it is through air it is called air resistance.<br />
31. 31. Fluid Friction<br />In this case, the waterfall is encountering air resistance on the way down, causing it to spread out and slow down.<br />It also experience friction upon striking the pool surface, causing it to splash and spread.<br />
32. 32. Friction is good…<br />Without friction we wouldn’t be able to walk, sit in a chair or drive safely. Everything would keep sliding and falling over.<br />We need friction between our feet and the ground or we would not be able to stand up.<br />When you are riding a bike and press the brakes, friction slows your bike down.<br />
33. 33. Friction is bad…<br />If you want to push something heavy, friction makes it harder to move.<br />Friction produces heat. Causing heat to build up is not always a good thing, especially inside a car engine.<br />We try to reduce the amount of friction in a car engine by adding oil.<br />
34. 34. Gravity<br />The attractive force between all objects in the universe<br />
35. 35. The greater the mass, the more gravity it has<br />Gravity<br />