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Action and Reaction Notes

Action and Reaction Notes. Newton’s Third Law of Motion. Action and Reaction.

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Action and Reaction Notes

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  1. Action and Reaction Notes Newton’s Third Law of Motion

  2. Action and Reaction • Newton’s Third Law of Motion: when one object exerts a force on a second object, the second one exerts a force on the first that is equal in size and opposite in direction. OR… for every action force there is an equal and opposite reaction force. • These forces always act in pairs. • These forces always act on DIFFERENT objects.

  3. Newton’s Third Law Examples: - jumping on a trampoline (you place a force on the trampoline which places an equal and opposite force back on you – causing you to go “up”) - jumping from a boat (you place a force on the boat which sends the boatbackward, but the boat places an equal and opposite force back on you causing you to move forward) - a rocket (gases are pushed out by the engine which placean equal and opposite force back on the rocket – causing it to fly)

  4. Action Force/ Reaction Force Diagram Reaction Force Action Force

  5. Momentum • Momentum: a property a moving object has because of its mass and velocity Momentum = mass x velocity p = m x v • Momentum is measured in kg x m/s • Example: - two trucks may have the same velocity, but the one that has the greater mass will have greater momentum.

  6. EXAMPLES of Momentum • If the velocity of a bus & a car traveling along the highway is equal, the bus will have more momentum because it has more mass. MORE LESS • If the mass of two bicycles and their riders are equal, the one that is moving at a greater velocity has more momentum because it is moving faster.

  7. Law of Conservation of Momentum • Law of Conservation of Momentum: the total amount of momentum of a group of objects does not change unless outside forces act on the objects. • Example: Pool table - no balls moving = zero momentum - cue ball moving toward the group of balls has momentum - cue ball hits the group of balls and scatters the balls; spreads the total momentum out amongst all of the moving pool balls

  8. Law of Conservation of Energyapplied to momentum • Energy cannot be created or destroyed, but can changeforms. • Momentum is a result of an object’s motion. • Energy can be transferred from one moving object to another in a collision. • All energy within the system can be accounted for because any energy left after the transfer of energy from one object to another in a collision changes to different forms of energy.

  9. EXAMPLES In a game of billiards or pool: • Potential energy for the motion of balls on a pool table is stored in the person holding the stick as he/she prepares to hit the ball. • Most of this energy is changed to kinetic energy (of the moving cue ball). • When the cue ball collides with the group of balls causing them to scatter and spread out, kinetic energy of the cue ball is shared among all moving balls. • Remaining energy is changed to sound, heat from friction, etc. • In conclusion, all potential energy originally stored in the person holding the pool stick is used. • Therefore, no energy is created or destroyed.

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