02-03-2011

Applying Newton’s Second Law

Today’s objective is to apply what we know about acceleration and mass to calculating Net Force.

Lets Review . . .1)What is acceleration? What formula do

we use to calculate acceleration? What units do we use to measure acceleration?

2)Apply – Dan is standing at his locker C hall. The last bell rings and he knows Mrs. Dion will kick his butt if he is late. Dan quickly runs down C hall toward E hall at 5 m/s in 45 seconds. What is Dan’s acceleration?

• Newton’s first law of motion states that the motion of an object changes only if an unbalanced force acts on the object.

• Newton’s second law of motion describes how the forces exerted on an object, its mass, and its acceleration are related.

Review of Newton’s Laws

• What’s different about throwing a ball horizontally as hard as you can and tossing it gently?

Force and Acceleration

When you throw a ball as hard as you can, you are adding more force so it has a greater change in velocity over time (acceleration).

• A hard-thrown ball has a greater acceleration than a gently thrown ball.

• So, the greater the force the greater the acceleration.

Force and Acceleration

Summary Point:

• If you throw a softball and a baseball as hard as you can, why don’t they have the same speed?

• The difference is due to their masses.

Mass and Acceleration

• If it takes the same amount of time to throw both balls, the softball would have less acceleration.

Mass and Acceleration

• The acceleration of an object depends on its mass as well as the force exerted on it.

• Force, mass, and acceleration are related.

Summary Point:

Newton’s second law of motion states that the acceleration of an object is in the same direction as the net force on the object, and that the acceleration can be calculated from the following equation:

Applying Newton’s Second Law

If the mass of a helicopter is 4,500 kg, and the net force on it is 18,000N, what is the helicopter’s acceleration?

You push a friend on a sled. Your friend and the sled together have a mass of 70 kg. If the net force on the sled is 35N, what is the sleds acceleration?

Check your work. Make sure you have set up the formula, plugged in the numbers, and answered with the correct

units.Break Time when you are done and have had your

work checked!

In order to solve for mass in these problems:m = Fnet / a

Try . . .

A car is being pulled by a tow truck. What is the car’s mass if the net force on the care is 3,000 N and it has an acceleration of 2.0 m/s/s?

To solve for the Net Force . . .

Fnet = m x a

Try . . .What is the net force on a dragster

with a mass of 900 kg it its acceleration is 32.0 m/s/s?

1) Friction-2) Static friction-3) Sliding friction-4) Rolling friction-5) Air resistance-