Newton’s Second Law

Coach Dave EdingerJ. C. Booth Middle

SchoolPhysical Science (8A)

Mrs. Coach

Ed

R-O-C-K-S !!!

Newton’s 1st law REVIEW

Summarize what the law states.

What does an object at rest need for it to move?

What is another name for Newton’s first law of motion?

What is inertia?

What causes a moving object to stop moving?

The (more/less) mass an object has, the harder it is to move.

The (more/less) mass an object has, the easier it is to move.

NEWTON’S second law

The acceleration of an object depends on the mass of the object and the amount of force applied.

VOLUNTEERS!!!!!TWO “pushers” of similar sizeONE small 8th graderONE big 8th grader

Part 1: Acceleration depends on massAcceleration of an object

decreases as its mass increases.

Acceleration of an object increases as its mass decreases.

Which would be easier to push?

WHY?

Part 2: Acceleration depends on forceAcceleration of an object increases

as the force on it increases

Acceleration of an object decreases as the force on it decreases

VOLUNTEERS!!!!!

ONE to sit in chairONE to push chair

Newton’s law with MATH

Formula: Force = mass • acceleration

UNITS

accleration: m/s² (meters per second squared)

force: N (Newtons)mass: kg

(kilograms)

F

m a

Tricky…tricky….

You don’t use Newtons to find acceleration in this formula

1 N = 1 kg∙m/s²

So…4 N = 4 kg∙m/s²And….500 N = 500 kg∙m/s²

And 395 N = ?

Newton and math exampleMass of apple: 0.102kgForce: 1N

What is the acceleration?

Newton and math exampleMass of apple: 0.102kgForce: 1N

What is the acceleration?a = F/m

Newton and math exampleMass of apple: 0.102kgForce: 1N

What is the acceleration?a = F/m

a = 1N / 0.102kg

Newton and math exampleMass of apple: 0.102kgForce: 1N

What is the acceleration?a = F/m

a = 1N / 0.102kga= 1 kg∙m/s² / 0.102kg

a= 9.8 m/s2

Practice

What is the acceleration of a 7kg mass if a force of 68.6 N is used to move the mass?

a = F / m

Practice

What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth?

a = F / ma = 68.6 N / 7 kg

Practice

What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth?

a = F / ma = 68.6 N / 7 kg

a = 68.6 kg • m/s2 / 7 kg

Practice

What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth?

a = F / ma = 68.6 N / 7 kg

a = 68.6 kg • m/s2 / 7 kga = 9.8 m/s2

Practice

What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth?

a = F / ma = 68.6 N / 7 kg

a = 68.6 kg • m/s2 / 7 kga = 9.8 m/s2

Practice

What is the acceleration of a 7kg mass if a force of 68.6 N is used to move it toward earth?

a = F / ma = 68.6 N / 7 kg

a = 68.6 kg • m/s2 / 7 kga = 9.8 m/s2

Challenge question

What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ?

Challenge question

What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ?

F = ma

Challenge question

What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ?

F = maF = 1250 kg • 40 m/s2

Challenge question

What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ?

F = maF = 1250 kg • 40 m/s2

F = 50,000 kg • m/s2

Challenge question

What force is necessary to accelerate a 1,250kg car at a rate of 40 m/s² ?

F = maF = 1250 kg • 40 m/s2

F = 50,000 kg • m/s2

F = 50,000 N

Another challenging question

Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration?

Another challenging question

Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration?

F = ma

Another challenging question

Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration?

F = maF = 175 kg • 2 m/s2

Another challenging question

Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration?

F = maF = 175 kg • 2 m/s2

F = 350 kg • m/s2

Another challenging question

Zookeepers carry a stretcher that holds a sleeping lion. The total mass of the lion and the stretcher is 175 kg. The lion’s forward acceleration is 2 m/s². What is the force necessary to produce this acceleration?

F = maF = 175 kg • 2 m/s2

F = 350 kg • m/s2

F = 350 N