Push or Pull Investigating Newton’s 2 nd Law of Motion Sports – Ch. 2, Act. 2

What do you think? Moving a football one yard to score a touchdown requires strategy, timing, and many forces. What is a Force? A force is a push or a pull. Can the same force move a bowling ball and a ping pong ball? Yes, but how will they be different?

A Push or Pull A force can be a push: A force can be a pull:

How do Forces Act on Objects? A force can cause an object to speed up (accelerate). A force can cause an object to slow down (accelerate negatively). A force can cause an object to change direction.

Force and Mass Newton determined that the acceleration of an object is directly proportional to the force applied to move it and inversely proportional to the mass of the object. What does this mean? 1. As mass increases and the force is held constant, the rate of acceleration will decrease. 2. As the amount of force is increased while keeping the mass constant, the acceleration will increase.

Inverse Relationship Direct Relationship Acceleration Newton’s 2 nd Law Newton’s 2 nd Law in relation to the acceleration of objects a = F /m Slope = mass More Force = More Acceleration Acceleration More Mass = Less Acceleration

Newton’s 2 nd Law and the v vs. t Graph Newton’s 2 nd Law indicates that a constant force applied to an object will cause the speed to change at a constant rate. Time The slope (m) of the line equals the acceleration of the object.

Force Constant / Increasing Mass If the force is held constant and the mass is increased from m 1 to m 2, what would a velocity vs. time graph look like? Time m1m1 m2m2 As the mass increases, the rate of acceleration will decrease. m 2 > m 1

Mass Constant / Increasing Force If the mass is held constant and the force is increased from F 1 to F 2, what would a velocity vs. time graph look like? F2F2 Time F1F1 As the force increases, the rate of acceleration will increase. F 2 > F 1

An Alternate View Newton’s 2 nd Law of Motion F = m a Where: F = force m = mass a = acceleration The force required to accelerate a 1 kg object 1 m/s 2 is called the Newton. 1 N = 1 kgm/s 2

Mass vs. Weight Mass is a measure the amount of matter an object contains, and is measured in kilograms. Weight is a measure of the force on a object due to the acceleration of gravity. F g = mg

Example 1: Newton’s second Law: F = m x a Sprinter beginning 100 meter dash ?70 kg5 m/s 2 Long jumper in flight 800 N?10 m/s 2 Shot put ball in flight 70 N7 kg? Ski jumper going down hill before jumping 400 N?5 m/s 2 Hockey player “shaving ice” while stopping -1,500 N100 kg? Running back being tackled ?100 kg-30 m/s N 80 kg 10 m/s 2 80 kg -15 m/s N

Example 2a: Why is the acceleration for the shot putter and long jumper 10 m/s 2 ? The key to this answer is the fact that they are in flight. While in flight, the shot put and long jumper act as projectiles. Gravity is the only force acting on them, and only in the vertical direction.

Example 2b: The force on the hockey player while stopping is negative. Should it be negative. Yes, because in order to stop, their must be a force that opposes the hockey player’s motion.

Positive Acceleration Time Relative Speed