Newton's 2nd Law

Newton's 2nd Law

F=m*a

Objectives:

^1. I understand the difference between acceleration and velocity.

^2. I can describe the relationship between acceleration and force.

^3. I can describe the relationship between acceleration and mass.

Newton's first law says that an object at rest stays at rest unless a force is added to change its motion. But what kind of change happens?

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The answer is acceleration.

Acceleration - rate at which velocity changes with time, in terms of both speed and direction.

Acceleration is different from velocity.

Velocity is the speed of something in a direction at a particular time.

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Acceleration is the CHANGE in velocity over a certain distance

Multiple Choice

A skydiver is moving downward with decreasing speed as her parachute opens.

Which statement describes the skydiver's motion?

• The skydiver is accelerating.

• The skydiver has a constant velocity.

Acceleration isn't just when somethings speeds up!

Multiple Choice

Which of the following boxes are accelerating? Select all that apply.

• A box of books that a woman is pushing across the floor with increasing speed.

• A box of jewelry that a girl is holding still in her lap.

• A box of cereal that is moving along a straight conveyor belt at a steady speed.

It's also when it slows down and changes direction.

Any change in velocity is a change in acceleration.

Draw

Draw an example of an object accelerating by speeding up, slowing down, or changing directions.

Remember, velocity is a vector

This means it contains speed and direction. So changing direction, even when staying at the same speed, is considered accelerating.

Newton's 2nd Law of Motion

acceleration of an object is directly proportional to the net force and inversely proportional to its mass. 

Newton's 2nd Law of Motion

f=m*a

Force = mass * acceleration​​

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acceleration of an object is directly proportional to the net force and inversely proportional to its mass. 

Newton's 2nd Law of Motion has 3 parts

¹Acceleration is the result of unbalanced forces.

²A larger force makes a proportionally larger acceleration.

³Acceleration is inversely proportional to mass.

¹Acceleration is the result of unbalanced forces.

Unbalanced forces are required for motion and acceleration to occur. A net force is when the forces add up to more than zero.

Open Ended

Can you think of an example where an unbalanced force creates acceleration and a balanced force doesn't?

On the other hand, balanced forces result in no motion, or no acceleration.

²A larger force makes a proportionally larger acceleration.

​The relationship between force and acceleration.

²A larger force makes a proportionally larger acceleration.

A larger force on something with the same mass, leads to a larger acceleration.

²A larger force makes a proportionally larger acceleration.

This is like saying Fernando Tatis Jr. will accelerate the ball greater than I will, because he will hit the same ball with a much greater force.

²A larger force makes a proportionally larger acceleration.

This is the relationship between force and acceleration. As force increases, acceleration does at the same rate.

³Acceleration is inversely proportional to mass.

*INVERSELY kind of means opposite. This means that acceleration is oppositely related to mass. When one goes up, the other goes down. This is their relationship.

³Acceleration is inversely proportional to mass.

For example, this guy easily lifts this little car and knocks it over. But, if we increase the mass and made it a large truck and he used the same force, it wouldn't accelerate as much. This is because acceleration and mass are inversely related.

Draw

Circle the graph that represents the relationship between force and acceleration.

Draw

Circle the graph that represents the relationship between mass and acceleration.

³Acceleration is inversely proportional to mass.

REMEMBER: as mass increases, so does the object's inertia.

SINCE inertia is an objects resistance to change in velocity...

THEN an increase mass would also resist acceleration.

KEY POINTS!

^1. The net force is what causes acceleration.

^2. If there is no acceleration, the net force must be zero.

^3. If there is acceleration, there must also be a net force.

^4. Force causes acceleration.

^5. Mass resists acceleration.