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# Forces

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### Forces

1. 1. May the Force be with you This is funny
2. 2. Definition Force:  any push or pull on an object (its that simple) ….But be careful! Commonly students will think forces have to come from living or moving things.  Not true.  Gravity pulls a chair to the floor and the floor pushes back.
3. 3. Forces can cause:   1) speeding up 2) slowing down 3) change in direction        IN OTHER WORDS FORCES CAN* CAUSE: ACCELERATION*(but they don’t always cause acceleration!)
4. 4. Balanced forces:   When all the forces cancel each other out= no net change in motion  (no acceleration!)
5. 5. Unbalanced forces:  Two or more forces that work and add together to change motion  (cause acceleration) Example of a canoe being rowed on a river on a windy day http://rt210.sl.psu.edu/simulations/physlets/force_table.html
6. 6. Vectors Forces are vectors Vectors are ____________with ______________ Which one is a vector: Speed or Velocity?
7. 7. Newtons In the metric system, the unit of force is the Newton. It can be used to quantify the pull or push of ANYTHING! What is correct: To weigh something in pounds, Newtons, or Kilograms?
8. 8.  balanced forcesexample:  You on a chair  you are pulled down by gravity and the chair pushes back on your butt.  Think about it....If you sat on the hard chair for three hours without moving, wouldnt you feel the chairs push?
9. 9. unbalanced forcesexample:  a rocket taking off the force of the engines is enough to overcome gravity and the rocket accelerates off the launch pad
10. 10. Questions Is it possible to have one balanced force? If so, draw as a vector diagram. Is it possible to have 2 balanced forces? If so, draw as a vector diagram. Is it possible to have 3 balanced forces? If so, draw as a vector diagram.
11. 11. More questions Can an object be in motion with balanced forces acting on it? Defend your answer. Can an object be stationary with unbalanced forces acting on it? Defend your answer.
12. 12. More…. Can you predict the motion of this box? Force: 5 N
13. 13. Friction:  a force; it causes negative acceleration (slows things down and makes them stop) (Can it also aid positive acceleration?) its mostly caused by: interaction of the matter that is in contact Also caused by differences in materials that are in contact.
14. 14. The Three Types of Frictionand Each One’s Properties 3 types Typical Examples Relative strength Sliding Strongest Book pushed on table Rolling Medium Car wheels Fluid Lowest Swimming or flying
15. 15. From mass to Force (Part II) Mass:  Amount of Matter in an object  Something is hard to move if it has more mass  Basically the “amount of stuff” found in something
16. 16. Inertia Objects with mass don’t like to move This property is inertia How is it measured?
17. 17. Weight Weight is a ___________ Caused by ___________ All atoms are pulled by gravity, so things with atoms have weight
18. 18. Speed and Velocity Rate of motion Velocity includes direction V= D/T (with direction) Units: Meters per second
19. 19. Momentum When things move faster, they become harder to stop And when they are more massive they are also harder to stop Momentum is like “inertia in motion” ρ=Mass times velocity Momentum is not a force, but it takes a force to stop momentum……… Units: Kilogram Meters per second
20. 20. Acceleration When speed or direction changes Only a force can cause acceleration Change in speed divided by time Or Ending speed – Starting speed TimeUnits: Meters per second squared
21. 21. Acceleration when falling On earth this is at a rate of 9.8 m/s/s This is a fast rate of acceleration What affects this acceleration during the fall?
22. 22. Finally………Force Any push or pull Forces can accelerate a mass Force equals mass times acceleration F= MA Units: Kilogram meters per second squared (or Newtons)
23. 23. Weight is a Force On earth you calculate weight byMultiplying mass (in Kg) times acceleration due to gravity (9.8 m/s/s) This will give you weight in Newtons Weight= mg If you wanna turn your mass into weight….don’t forget to multiply by 9.8 (m/s/s)
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