Transcript File
Chapter 12 Section 3 Notes Force: a push or pull on an object Force is not something that an object possesses An object only exerts force on another object But when that object exerts its force, the second object always exerts one back Every force is part of a pair of forces An interaction We call this a Force Pair One is called an Action The other is a Reaction Whenever one object exerts a force on a second object, the second object exerts a force that is… ◦ Equal in Magnitude ◦ Opposite in Direction To every action there is an equal and opposite reaction Wall hits fist Hey! Why don’t you try some on your own? When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. Forces are equal in size and opposite in direction ◦ Hand against a wall. Forces do not cancel if they act on different objects Forces only cancel if they act of the same object Momentum: Property possessed by an object. Directly proportional to mass of the object. Directly proportional to velocity of the object at that moment. (instantaneous motion) Momentum is abbreviated as p (Greek ‘rho’) m is the symbol for mass v is the symbol for velocity Momentum is the product of the mass & the velocity of an object Calculate the momentum of a 12 kg object traveling at 4 m/s. P=? m = 12 kg v=4m s p = mv p = 12 kg x 4 m s p = 48 kg x m = 48kgm s s Hyperphysics: calculate various momenta 1. Calculate the momentum of a 0.15 kg ball that is moving toward home plate at a velocity of 40m/s. 2. Which has greater momentum, a 2.0kg hockey puck moving east at 2.5m/s or a 1.3kg hockey puck moving south at 3.0m/s? 3. A track athlete throws a 2kg discus into a field with a velocity of 21m/s. What is the momentum of the discus? 4. Calculate the momentum of a 700g ball that is rolling down a ramp at 4.6m/s. Hey! That looks like Newton’s 2nd Law. Force = mass * acceleration Acceleration is the change in velocity over time So Newton’s 2nd Law could read Force = change in momentum Time p = mv F = ma Momentum Newton’s Second Law But we can use Dv for acceleration. Dt F = mDv = Dp Dt Dt OR F = Dp Newton’s second law as change in momentum over time. Dt Rearrange to a new form, FDt = Dp Impulse MomentumRelationship Momentum is the product of the velocity and mass of an object Momentum = mass X velocity So, the bigger it is and the faster it goes the greater the momentum. In a closed system, the loss of momentum of one object equals the gain in momentum of another object Therefore, momentum is conserved! Bill Nye!