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

Acceleration An unbalanced force causes something to accelerate.

Acceleration Acceleration is directly related to the size and direction of the force. It accelerates in the direction you push or pull it.

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

So….if you push twice as hard, it accelerates twice as much. In other words…. Small Force = Small Acceleration F a So….if you push twice as hard, it accelerates twice as much.

But there is a twist…. Acceleration is INVERSELY related to the mass of the object.

In other words…..using the same amount of force…. Small acceleration a Large Mass Large acceleration F a Small Mass

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

Newton’s Second Law The acceleration of an object depends on the mass of the object and the amount of force applied. F = ma Force = Mass x Acceleration

Newton’s Second Law Key Point #1: Increased force  increased acceleration Key point #2: Increased mass  decreased acceleration (for the same amount of force)

Golf Ball vs Ping Pong Ball - DEMO

Golf Ball vs Ping Pong Ball - DEMO They fall at the same time because… Gravity accelerates the two objects at equal rates

Sample Problem – Calculate the acceleration of an apple and watermelon when dropped off of a building. Mass = 1.02 Kg Force = 10 N Mass = .102 kg Force = 1 N

Sample Problem So the objects have equal acceleration – they both accelerate at -9.8m/s² (due t0 gravity)

Hmm… does this mean they would land at the same time if dropped off of a building?

Hmm… does this mean they would land at the same time if dropped off of a building? Why don’t we actually observe all objects falling at the same rate in Earth’s atmosphere?

Hmm… does this mean they would land at the same time if dropped off of a building? Why don’t we actually observe all objects falling at the same rate in Earth’s atmosphere? Air resistance slows down acceleration. Air resistance is a type of fluid friction. The amount of air resistance depends on the size and shape of the object. Example: Feather vs Apple

Practice Problems

Lab Instructions Measure the TIME it takes for the car to travel the distance of the counter PART 1: Pull with 1 oz fishing weight Put 100 grams in car Repeat with 500 grams PART 2: Put 500 grams in car Pull with 2 oz fishing weight

Let’s see it in action…

Lab Data PART 1: PART 2:

Lab materials

Lab set-up

Procedures Assemble the book and ramp (ruler) as shown in your diagram. Place the larger marble at the bottom of your ramp. Drop the smaller marble from the top of your ramp. Time how long it takes the larger marble to reach the end of the ramp. Record data below. Place the smaller marble at the bottom of the ramp. Drop the larger marble from the top of your ramp. Time how long it takes the smaller marble to reach the end of the ramp. Record data below.

Data Table

Have fun but… don’t lose your marbles! 