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Forces
- 1. What are Forces? October 20, 2014
- 2. What forces do you think are acting on you right now while you’re sitting in your seat?
- 3. There are forces acting on you all the time whether you know it or not! • Gravity is pulling you down • The ground is pushing you up • Air is squeezing you from every direction • Your body is pushing back at the air
- 4. When forces are balanced, they cancel out and you don’t notice them. But when forces don’t balance, things happen… THINK! What would happen if we took the force of gravity away?
- 5. A force is a PUSH or a PULL • Forces can cause an object to move, change speed, change direction, change shape, or stop • Forces have size and direction
- 6. • When you drop your pencil, gravity is pulling it to the ground • When you are walking around, your feet are pushing down onto the ground
- 7. Force Facts • Measured in Newtons (N) • Always act in pairs • Cannot be seen, but the effect can be seen • Measured using a spring scale
- 8. Measuring Force • How many Newtons will it take for me to drag your science binder across the desk?
- 9. Net Force Net force: the size of all the forces acting on an object • If two forces acting on an object are in the SAME direction, you ADD the forces together • If two forces acting on an object are in the OPPOSITE direction, you SUBTRACT the forces
- 10. Written with a magnitude and direction Ex: Force Net = 30 N
- 11. If two forces acting on an object are in the SAME direction, you ADD the forces together 50 N 75 N Net force =
- 12. If two forces acting on an object are in the OPPOSITE direction, you SUBTRACT the forces 500 N 100 N Net force =
- 13. Balanced Forces • Forces that cancel each other out • Net force = ZERO • There is no change in motion
- 14. Balancing your science textbook on your desk Force net =
- 15. Net force =
- 16. Unbalanced Forces • When forces acting on an object do not cancel out • Net force does not = zero • Produce a change in motion
- 17. Net force =
- 18. Checkpoint 1. What is the unit used for measuring a force? Newtons 2. What tool is used to measure forces? Spring Scale
- 19. 3. Find the net force 950 N 625 N
- 21. Review 1. Find the net force 600 N 600 N
- 22. 2. Find the net force 525 N 50 N
- 23. Forces that act against motion… If you kick a soccer ball on grass, what will start to slow it down?
- 24. The enemy of motion • Friction: force that occurs when 2 objects rub against each other • Always acts in the direction opposite to the direction of motion • Will slow the motion of an object or stop it • Creates heat
- 25. • Every object causes friction, some more than others • It may look smooth, but it is covered in tiny bumps and dents
- 26. • Friction can be beneficial • Everyday life would be a lot different without it • THINK! What would happen if the floor in the classroom was ice instead of carpet?
- 28. When would decreasing friction be beneficial?
- 29. Is it possible to pick up a bottle full of rice with just a pencil? YES!
- 30. 4 Types of Friction • Static friction • Sliding friction • Rolling friction • Fluid friction
- 31. Fluid Friction- Air Resistance • Caused by friction of the air against an object • Objects with more surface area experience greater air resistance and move more slowly
- 32. Gravity • Force that pulls objects towards each other • Law of gravitational force: The force of gravity depends on the distance between the objects and their masses
- 33. Which objects have the greatest force of gravity? A B C D A and C D and B B and C A and D
- 34. • Mass: the amount of matter in an object (g) • Weight: measure of the force of gravity on an object (N)
- 35. • All objects fall at the same rate towards the earth because gravity pulls on every object the same amount • Air resistance slows objects down What would hit the ground first, a pencil or a ball? What about a sheet of paper and a balled up sheet?
- 36. An object’s weight can change if you went from the earth to the moon, but your mass would stay the same. Ex: Gravity on moon is 1.622 m/s2
- 37. THINK! What would happen if we drop a feather and a hammer on earth? What if we were on the moon? Hammer-feather drop What is happening?
- 38. Zero G Experience http://www.gozerog.com
- 39. Checkpoint 1. Is your mass the same on earth and the moon? 2. Is your weight the same on the earth and moon? 3. What forces will effect a soccer ball that has been kicked?
- 40. StudyJams Video
Notas do Editor
- Demonstrate the spring scale by pulling object across table
- 400 N
- 5 N up (table) 5 N down (gravity) F net= 0 N
- 100 N 100 N F net = 0N
- 600 N 500 N F net = 100 N
- 475 N
- No matter how smooth an object might look, its really covered with millions of tiny jagged bumps and dents When 2 objects rub together, the tiny bumps snag each other and slow down the objects down
- No matter how smooth an object might look, its really covered with millions of tiny jagged bumps and dents When 2 objects rub together, the tiny bumps snag each other and slow down the objects down
- What could we do to stop us from sliding around the ice classroom?
- This experiment teaches about friction. Friction is the resistance you feel when one object is moved against another. When you’re walking outside on a snowy day, you might step on ice and slip. The ice is slippery because there is a low amount of friction between your feet and the ice. But if you sprinkle sand on the ice, you can walk without slipping – the sand increases the friction to make walking safer. When you stab the pencil into the rice and it “sticks”, the rice is packed against other grains of rice, with are all contained by the bottle. The friction between the rice and the pencil is strong enough to hold the pencil in place when you lift the bottle with it.
- Liquids and gases, like air, are considered fluids (free flowing-can flow and change shape) Paper ball and piece of paper demonstration
- We measure weight in pounds, but in physics when we are describing weight as a force, it is measured in newtons How hard is gravity pulling down an object down
- Would you weigh more on earth or the moon?