1. Newton’s Second Law of Motion How fast does it go?

2. Acceleration An unbalanced force causes something to accelerate. Remember acceleration is any change in speed or direction!

3. Acceleration Acceleration is directly related to the size of the force (mass) and the direction of the force. directionObjects accelerate in the direction you push or pull them.

4. In other words…. Large Force = Large Acceleration F a

5. Remember that… The more MASS an object has, the more INERTIA the object has. Bigger objects are harder to start & stop! Which vehicle has more inertia? Slide from www.science-class.netwww.science-class.net

6. Newton’s Second Law Newton, that brilliant genius, observed those “rules” of acceleration and came up with his second law of motion. It is both a formula & a law.

7. Newton’s Second Law net force massThe acceleration of an object depends on the net force acting on the object and the mass of the object! Force = Mass x Acceleration aka… F = ma and “The Law of Force” Measured in Newtons (N).

8. Units! Lets review some of our units… –The units used for mass are kilograms (kg) –The acceleration units are meters per second squared (m/sec 2 ). –One Newton = the force required to accelerate 1kg of mass at 1 meter per second per second….. –*So… 1N = 1kg x 1m/sec 2

9. GUiDeD PrAcTiCe! A 52kg water-skier is being pulled by a speedboat. The force causes her to accelerate at 2 m/sec 2. Calculate the force that causes this acceleration. Force = Mass x Acceleration in Newtons F = 52kg x 2 m/sec 2 F = 104 kg x m/sec 2 F = 104 N

10. INDEPENDENT PrAcTiCe! 1. What is the force on a 1,000 kg elevator acceleration at 2 m/sec 2 ? 1,000 x 2 = 2,000 N 2. How much force is needed to accelerate a 55 kg cart at 15 m/sec 2 ? 55 x 15 = 825 N 3. When the force on an object increases, how does the objects acceleration change? It increases.

11. 4. Suppose you know the acceleration of a shopping cart as it rolls down an aisle. You want to know the force it was pushed with. What other information do you need to know to determine this? The mass. 5. Suppose you doubled the force acting on an object. In what way could you change its mass to keep its acceleration constant? Double it.