1. Physics: Force

2. Physics Physics is the science of understanding forces A force is a push or pull. It has both direction and magnitude (strong/weak) General forces include gravity and friction Elastic forces include compression, tension, and torque

3. Gravity is a force that pulls towards the center of the Earth Gravity & Weight

4. Weight is a force that is a measure of gravity’s pull on an object Gravity & Weight Turkey Scale

5. To calculate the weight force of gravity’s pull on an object, multiply mass by gravity: 1.Convert mass in grams to kilograms (move the decimal to the left three places) 2.Multiply by gravity which on Earth is 9.8 Calculating Weight Force

6. The unit for all forces is the Newton (N) Named after Isaac Newton, the famous physicist Unit

7. If mass = 215 g force =.215 x 9.8 = 2.107 = 2.1 N Examples: If mass = 1.2 g force =.0012 x 9.8 = 0.01176 = 0.01 N

8. Gravity increases with mass Understanding Gravity Gravity decreases with distance Large Mass More Gravity Small Mass Less Gravity

9. Think of gravity as massive objects creating warps in the fabric of space Understanding Gravity

10. Understanding Gravity – Newton vs Einstein

11. Two forces are always opposing motion: –Gravity –Friction Gravity & Friction Oppose Motion

12. Gravity is a force that slows upward and trajectory (on a path) motion by pulling objects towards the Earth Gravity Opposes Motion Gravity slows upward motion Gravity slows forward motion

13. Gravity pulls all objects to the Earth at the same rate no matter if they are dropped or shot from a gun Gravity Opposes Motion

14. Friction is a force that opposes motion between touching surfaces Motion Force Friction Force Friction Opposes Motion It is hard to walk without friction

15. The space shuttle and meteors (shooting stars) have air friction between their surface and our atmosphere Friction Opposes Motion

16. Friction creates heat and wears out objects Hip Replacement Friction Opposes Motion

17. Lubrication, such as oil and grease, help reduce friction Friction Opposes Motion

18. There are two basic types of friction: static and kinetic. Static friction is the stronger force of the two. Friction Opposes Motion

19. Static friction occurs before movement takes place - it resists movement. Motion Force Friction Force Friction Opposes Motion

20. Kinetic friction occurs during movement - it tries to slow or stop movement. Motion Force Friction Force Friction Opposes Motion

21. Example Question What two forces oppose the motion of this bike? Motion Force Friction Force

22. Elastic Forces Compression Forces come together from opposite directions (crushing a can) Don’t try this at home!

23. Forces applied in opposite directions (tug of war) Elastic Forces (continued) Tension

24. Elastic Forces (continued) T o rque A twisting force (the ‘O’ in torque)