1. Chapter 12 Forces and Motion

2. Force Force: a push or a pull that acts on an object A force can cause a ___________ to move, or a ____________to accelerate Resting object Moving object

3. Units of Force Force is measured in Newtons (N) One Newton is the force that causes 1 kilogram mass to accelerate at a rate of one meter per second each second (1 m/s 2 )

4. Bellwork What is the unit we use to measure force?

5. Representing Force Arrows may be used to represent the direction and strength of a force Direction of arrow represents direction, length represents magnitude

6. Combining Force Net Force: the overall force acting on an object after all forces are combined Forces moving in the same direction are added Forces moving in opposite directions subtract from one another

7. Net Force?

9. Speed? What is the speed of a shark swimming 30 meters in 6 seconds? A.180 m/s B.5 m/s C.36 m/s D.24 m/s

10. Net Force

11. Balanced Forces When the forces on an object are balanced, the net force is zero and there is no change in the object’s motion

12. Balanced Forces

14. Unbalanced Forces When unbalanced forces are opposite directions, the net force equals the size of the larger force minus the size of the smaller force

16. Friction Friction: a force that opposes the motion of objects that touch as they move past each other – Includes solids touching each other – Four types are Static, Sliding, Rolling, Fluid

17. Static & Sliding Static: friction force that acts on objects that are not moving Sliding: friction force that opposes the motion of of a moving object

19. Rolling Friction Rolling Friction: The friction that acts on rolling objects Can be up to 1000 X less than static or sliding friction! Why do we use wheels to get around easier?

20. Fluid Friction Fluid Friction: Force opposing motion of an object through a fluid – Same force acting in fluids and air – Known as air resistance for objects moving through air

21. Friction https://www.youtube.com/watch?v=VUfqjSee Zng https://www.youtube.com/watch?v=VUfqjSee Zng

22. Gravity Earth’s gravity acts downward toward the center of the Earth

23. Falling Objects Both gravity and air resistance affect the motion of a falling object. Take two pieces of paper Crumple one piece Stand up Drop both pieces at the same time Write in your notebook how gravity and air resistance worked on these two objects

24. Falling Objects Gravity causes objects to accelerate downward Air resistance acts in the direction opposite to the motion and reduces acceleration

25. Terminal Velocity Gravity and air resistance work opposite each other Although objects in free-fall accelerate at an increasing rate, air resistance is greater the faster the velocity Eventually, gravity and air resistance will reach a balance and the object will reach terminal velocity

26. Terminal Velocity Terminal Velocity: the constant velocity of a falling object when the force of air resistance equals the force of gravity https://www.youtube.com/watch ?v=p0IZsfzDS4s https://www.youtube.com/watch ?v=p0IZsfzDS4s

27. Projectile Motion Projectile Motion: the motion of a falling object after it is given an initial forward velocity Objects of different mass will fall at the same rate Objects with a projectile motion will fall at the same rate as those without.

28. Talk with your partner for a minute about the following question: Will a bullet dropped from a certain height hit the ground at the same time as a bullet shot from a gun at the same height?

29. Myth Busters https://docs.google.com/file/d/0Bzs- X_4Ods2dbHNRNS1OZVpmbG8/edit https://docs.google.com/file/d/0Bzs- X_4Ods2dbHNRNS1OZVpmbG8/edit

30. Newton’s Laws Newton’s First Law: the state of motion of an object does not change as long as the net force acting on the object is zero

31. Inertia Objects at rest stay at rest Objects in motion stay in motion Inertia: the tendency of an object to resist a change in its motion This is why car accidents are so dangerous…the car stops, but your body has inertia and wants to continue in its forward motion

32. Inertia https://www.youtube.com/watch?v=6gzCeXD hUAA https://www.youtube.com/watch?v=6gzCeXD hUAA

33. Newton’s Second Law: The acceleration of an object is equal to the net force acting on it divided by the objects mass So, doubling an objects mass reduces its acceleration by half

34. Newton’s Second Law https://www.youtube.com/watch?v=iwP4heW Dhvw https://www.youtube.com/watch?v=iwP4heW Dhvw

35. Section 3 Newton’s 3 rd Law Newton’s 3 rd Law: whenever one object exerts a force on a second object, the second object exerts an equal and opposite reaction force on the first object