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A Tug of War - Force and Motion

A double approach to force and motion. Approach 1 - Derivative Units i.e. Speed = distance/timeVelocity = distance(direction)/timeAcceleration = speed/timeApproach 2 - Newton's LawsInertia, F=ma, equal and opposite reaction. . Newton's Laws as a tug of War. Consider a tug of warA flag is h

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A Tug of War - Force and Motion

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    1. A Tug of War - Force and Motion Ross Durand GGUSD November 6, 2002

    2. A double approach to force and motion Approach 1 - Derivative Units i.e. Speed = distance/time Velocity = distance(direction)/time Acceleration = speed/time Approach 2 - Newton’s Laws Inertia, F=ma, equal and opposite reaction

    3. Newton’s Laws as a tug of War Consider a tug of war A flag is held between two ropes, pulled by opposite sides What results????

    4. What if no one was tugging? What results????

    5. Why does the flag stay still? We call the tendency of a still object to stay still Inertia (Law number 1) This also applies to moving objects wanting to continue moving (we’ll discuss this later)

    6. Just one tug? What if only one side was pulling? Result - The Flag would move quickly to the right hand side.

    7. Just one tug?(part two) What if there were twice as many people pulling? Result - The Flag would move quickly to the right hand side. More quickly? How much?

    8. Why does it move faster? Adding more force increases the acceleration F=ma (Law number 2) (this also means you have to pull harder if there are more people on the other end of the rope)

    9. Two tugs again. Twice as many on one side What results now?

    10. What are we actually pulling on? We’re not pulling directly on the flag, are we? The rope is. So we’re pulling on the rope. What if you greased the rope?

    11. Greased rope. What happened to the size of the force on the greased side? It decreases, why?

    12. Friction Friction is a force which resists motion. When hands are clasped on a rope, you are hoping for a lot of frictional force, so that your hands do not move relative to the rope. The grease reduces the friction

    13. Where are the forces?

    14. What happens at the foot?

    15. Why doesn’t the foot move? For every action (force) there is an equal and opposite reaction (force). Law number three (If opposing forces are not equal, motion occurs, but this does not violate this law)

    16. Tug of war so far Inertia - the flag would not move except we pull on it. F=ma - more force causes a larger change in motion Equal and opposite - friction at the foot shows that the ground pushes back on the foot pushing on it.

    17. Variables so far Size of force Direction of force

    18. Where are the forces?

    19. How long do you pull? What happens when you stop pulling? Result - ?????

    20. How long do you throw? What happens when you stop throwing a ball? Result - ?????

    21. Why does a ball stop? At least three reasons Air friction? Gravity? Friction with the ground?

    22. Does it depend what kind of ball? Why use a wiffle ball? Increases air friction Results in hitting the ground sooner

    23. How is the ball like a tug of war? Both begin with inertia the ball is moving, the flag is still. The ball is moving, friction is “pulling” the other direction.

    24. What about a wiffle tug of war? Both begin with inertia the ball is moving, the flag is still. The ball is moving, friction is “pulling” the other direction.

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