Newton’s Second Law of Motion

But first, Let’s Review…. A bowling ball and a volleyball are rolling towards you. Which would be easier to stop? Explain your answer. A. You would have to exert a greater force on the bowling ball to make it stop. The bowling ball has more inertia than the volleyball because it has more mass.

You are pushing a cart with a box on top and come to a sudden stop. What happens to the box on top? Explain your answer The box on top will keep moving, at a constant speed, in the same direction. The inertia of the boxes causes them to keep moving even after the cart stops.

A Bonus Lesson A car traveling at 85 mph crashes head-on with something solid, crumples, slows and finally stops within 0.1s. Anyone in the car not wearing a seatbelt continues to move forward at the same speed the car was traveling (85 mph), slamming into the windshield, dashboard etc. Note: 85mph is about the speed falling from a three-story building. Bonus Lesson: Always wear your seatbelt!

Second Law of Motion Second Law of Motion: The acceleration of an object is dependent upon the force acting upon the object and the mass of the object.

Second Law of Motion Newton’s Second Law can be written as the equation: F = ma or Force = mass x acceleration F = force (N) m= mass (kg) a = acceleration (m/s/s or m/s 2 ) 1N = 1kg. m/s 2

Second Law of Motion This equation demonstrates the following two important relationships between force, mass and acceleration:

Second Law of Motion 1. The greater the force on an object, the greater the acceleration of an object. (Increase Force, Increase Acceleration) Example: In baseball, if I hit a ball as hard as I can, the ball accelerates more than if I was trying to bunt the ball.

Second Law of Motion 2. The greater the mass of an object, the smaller the acceleration. (Increase Mass, Decrease Acceleration) Example: In baseball, if I hit a 50 gram ball and a 25 gram ball with the same force, the 50-gram ball would go slower than the 25 gram ball because it has a greater mass.

Second Law of Motion Acceleration is directly proportional to the force: *you push twice as hard and it accelerates twice as much. (Increase Force, Increase Acceleration)

Second Law of Motion Acceleration is inversely proportional to the mass: *If it gets twice the mass, it accelerates half as much. (Increase Mass, Decrease Acceleration)

Use the TRIANGLE

Calculate Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's 2nd Law, you can compute how much force Mike is applying to the car. (hint: since you are trying to find force, use the equation F=MA)

Calculate BOB's van, which weighs 2,000 kg, is out of gas. BOB is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's 2nd Law, you can compute how much force Bob is applying to the van.

Let’s Practice Don’t Forget to use your triangle!