Do Now: What causes acceleration?

Section 2.2 –Day 1Define and calculate

acceleration.Explain the

relationship between force, mass, and acceleration.

Determine mass, acceleration and force given two of the quantities.

accelerationdeceleration

Objective: using the acceleration formula, practice calculating different variables.

Homework: Read Section 2.2 and complete worksheet.

Do Now: what would be the formula to solve for time if you were given acceleration and both initial and final speeds?

A skater increases her velocity from 2.0 m/sec to 10.0 m/sec in 3.0 seconds. What is the skater’sacceleration?

Use a = v2 – v1

tA car accelerates at a rate of 3.0 m/sec2. If its

original speed is 8.0 m/sec, how many seconds will it take the car to reach a final speed of 25.0 m/sec?

Use: t = v2 – v1

a

HOMEWORK

READ SECTION 2.2 AND COMPLETE WORKSHEET.

BrainPOP | Acceleration

Section 2.2 Day 2

DO NOW: DEFINE THE TERM NET FORCE!

Section 2.2 –Day 2

Explain the relationship between force, mass, and acceleration.

Determine mass, acceleration and force given two of the quantities.

VocabularyNewton’s 2nd Law

NEWTON’S SECOND LAW

States the stronger the net force on an object, the greater its acceleration. It also says that the greater the mass, the smaller the acceleration for a given net force.

Force causes acceleration, and mass resists acceleration.

Newton's first law tells us that a force is required to accelerate an object. Newton's second law answers the question about how much force is required. Have you ever tried to move a car? Which would be easier an 18 wheeler or a VW bug?

The key is the mass.

The mass of the truck is many more kilograms than the mass of the VW. So it is much harder to accelerate the more massive truck; it takes more force.

Notice that the difference is mass not size. For example a very large bag of feathers might be as large as a car but relatively easy to push. Feathers are not very tightly squeezed, so a large bag of feathers will still have a relatively small mass. It is takes less force to accelerate a bag of feathers the size of a car than the car. Mass and size are different things and the force needed to accelerate something depends on the mass not the size.

What does this mean????

If you want to calculate the acceleration, first you need to modify the force equation to get a = F/m. When you plug in the numbers for force (100 N) and mass (50 kg), you find that the acceleration is 2 m/s2.

Notice that doubling the force by adding another dog doubles the acceleration. Oppositely, doubling the mass to 100 kg would halve the acceleration to 2 m/s2.

If two dogs are on each side, then the total force pulling to the left (200 N) balances the total force pulling to the right (200 N). That means the net force on the sled is zero, so the sled doesn’t move.

Net forces

This is important because Newton's second law is concerned with net forces. We could rewrite the law to say: When a net force acts on an object, the object accelerates in the direction of the net force. Now imagine that one of the dogs on the left breaks free and runs away. Suddenly, the force pulling to the right is larger than the f orce pulling to the left, so the sled accelerates to the right.

Simply put…

Newton's second law tells us that the more massive an object is, the more force is needed to accelerate it.

HomeworkComplete worksheet

and problems 3-7 page 55.