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# Force and motion

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### Force and motion

1. 1. Motion & Forces
2. 2. Speed & Velocity • Speed - the rate of change in position over time (distance/time) • Instantaneous speed • Average speed • How is velocity different from speed? Velocity describes both speed and direction
3. 3. Change in Velocity What makes an object change velocity?
4. 4. Force • Push or Pull • Forces can cause a change in velocity • Examples: Gravity Magnetism Friction
5. 5. Balanced Forces Forces that – act on the same object – are opposite in direction – are equal in size
6. 6. Balanced Forces Book on table 1. Weight of the book is downward force caused by gravity 2. Table pushes back with an equal and opposite force Net force is zero
7. 7. Unbalanced Forces Forces that are NOT opposite and equal What do they cause? CHANGE IN VELOCITY ACCELERATION
8. 8. Friction Force that opposes motion between 2 surfaces Depends on the: • types of surfaces • force between the surfaces
9. 9. Types of Friction • Static Friction: (Couch Potato) – Force between objects at rest • Sliding Friction: (Ice skating) – Solid surfaces slide over each other • Rolling Friction: (Rollerblading) – An object rolls over a surface. • Fluid friction: (Submarine) – An object moves through a fluid
10. 10. Friction Friction is greater... –between rough surfaces –when there’s greater force between surfaces (such as more weight)
11. 11. Lubricant Changes sliding friction into fluid friction
12. 12. Friction Is friction always bad?
13. 13. Gravity The attractive force between all objects in the universe
14. 14. Acceleration of Gravity Near the surface of the earth the acceleration due to gravity is 9.8 m/s/s
15. 15. Newton’s 1 Law st An object at rest remains at rest and an object in motion will continue moving at a constant velocity unless acted on by unbalanced forces.
16. 16. Newton’s Laws of Motion
17. 17. Newton’s 1 Law st INERTIA • tendency of an object to resist any change in its motion • increases as mass increases
18. 18. Newton‘s 2 nd Law If more force is applied, an object will be accelerated _____ more
19. 19. Newton’s 2 nd Law • More force means more acceleration • More mass means less acceleration Force = mass X acceleration F = ma
20. 20. Newton’s 3 rd Law For every action, there is an equal and opposite reaction. Forces occur only in pairs – Act on different objects – Equal and opposite
21. 21. Newton’s 3 rd Law The hammer exerts a force on the nail to the right. The nail exerts an equal but opposite force on the hammer to the left.
22. 22. Momentum
23. 23. Terminal Velocity The final speed of a falling object.
24. 24. Terminal Velocity Air resistance is offsetting the the weight of the object
25. 25. Forces End
26. 26. Force Aristotle's idea: For an object to move at a constant speed, a constant force must be applied.
27. 27. Force Newton’s idea: An object moving at a constant speed will continue at that speed without additional force being applied.
28. 28. Balanced Forces