Use the Force…

1. Use the Force… A long time ago In a classroom far, far away, A group of future scientists gathered To discuss what forces can do for them. KL Physics 09

2. Use the Force…to make things happen • Force can make objects move • Force can change how things move • Force can change the direction of motion A force is a push or pull.

3. Use the Force…to make things happen Dynamics is the study of why objects move. A push or pull is called a contact force. Field forces exist in space and can be detected, but they don’t require contact (example: gravity).

4. 4 types of forces • Strong Nuclear Forces • Weak Nuclear Forces • Electromagnetic Forces • Gravitational Forces

5. Force! • Is a vector • Symbol: F • SI unit: Newtons (N) • 1N = 1kgm/s2

6. Newton’s 3 Law of Motion 1st Law of Motion – Law of Inertia An object at rest stays at rest and an object with constant velocity continues with that constant velocity unless an unbalanced force acts on it. Example: A car won’t turn on an icy road.

7. Newton’s 3 Law of Motion 2nd Law of Motion – Law of Acceleration The acceleration of an object is directly proportional to the unbalancedforce acting on it and is inversely proportional to the mass of the object. Fnet = ma Fnet and a point in the same direction Fnet is the resultant or unbalanced force.

8. Newton’s 3 Law of Motion 3rd Law of Motion – Law of Action and Reaction For every action there is an equal and opposite reaction. Action/Reaction forces are always in pairs that act on two different objects.

9. Example of 3rd Law Action/Reaction Pair Hammer hitting a nail Equal and opposite

10. Force is a Vector. It is drawn as an arrow. The length represents the magnitude. The arrow points in the direction of the vector.

11. Force is a Vector. • Examples of ways to describe forces: • 20 lbs to the right • 115 N, 45 degrees south • 35 N northeast • 10 lbs 30 degrees below the horizontal.

12. Force, F, is a Vector. The effect a force has on an object depends on the force’s magnitude (size) and it’s direction.

13. Force, F, is a Vector. Same magnitude, different direction = different force! Start

14. Balanced Forces Equal in size. They cancel each other out. No movement or change in movement occurs. Unbalanced Forces Not equal in size. The do not cancel each other out. An object will change speed or direction. Balanced and Unbalanced Forces

15. Net Force • Net force is adding all of the forces together Balanced = Net Force of 0 Newtons Unbalanced = Net Force of Non-zero We will talk about this more when we get to FREE BODY DIAGRAMS (FBD’s) YEA!!!

16. Imagine playing Tug-of-war… What happens when… You and your friend pull with the same force? You pull harder than your friend? Balanced and Unbalanced Forces

17. Balanced and Unbalanced Forces Imagine playing Tug-of-war… What happens when… You and your friend pull with the same force? Neither of you moves in either direction. (Balanced) You pull harder than your friend? Your friend moves towards you even though they are pulling the other direction. (Unbalanced)

18. FBD Example: Book Sitting on a table We will do more examples in class next time!

19. MAY THE m x a be with you!