Newton’s 2nd Law

Physics

October 25/26

Objectives

1. State the relationship between acceleration, mass and net force

2. Evaluate how the relationship between acceleration, mass, and net force affect motion

3. State and explain Newton’s second law of motion

4. Solve using the equation F = ma

What is Newton’s 2nd Law

TopicNewton’s second law

FactsThe acceleration

produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object (Hewitt 60).

What!?

Topic

Let’s put Newton’s 2nd Law in our own words

Facts• Force and acceleration are

proportional and mass and acceleration are inversely proportional

• The equation is F = maF = force (N)

m = mass (kg)

a = acceleration (m/s2)

..

How about a little more clarification

Topic

What does

F = ma tell us?

Facts• When mass is

constant, Force and acceleration are directly proportional to each other– As force increases so

does acceleration

– As force decreases so does acceleration

How about a little more clarification

Topic

What does

F = ma tell us?

Facts• When force is

constant, Mass and acceleration are inversely proportional to each other– As mass increases,

acceleration decreases

– As mass decreases, acceleration increases

A little more clarification

• Watch the video to hear Newton’s 2nd law one more time.

• Newton's Second Law Explained

Class Activity Explainedpage 59

Topic

Why are more massive objects harder to move?

Facts

• More massive objects have more inertia

Class Activity Explainedpage 59

TopicHow is the mass of

an object related to acceleration when force is constant?

Facts• Mass and

acceleration are inversely proportional. – More mass means

less acceleration – less mass means

more acceleration

Class Activity Explainedpage 59

TopicIf you want objects of

different masses to have the same acceleration, what must you do?

Facts

• You must apply more force to the more massive object

More Practice with Newton’s 2nd law

Topic

How much force, or thrust must a 30,000 kg jet plane develop to achieve an acceleration of 1.5 m/s2?

Facts

Knownm = 30,000 kga = 1.5 m/s2

Unknown

F

Equation

F = ma

SolveF = (30,000kg)(1.5 m/s2)

45,000 N

More Practice with Newton’s 2nd law

Topic

What acceleration is produced by a force of 2000 N applied to a 1000 kg car?

Facts

KnownF = 2000 Nm = 1000 kg

Unknowna

EquationF = ma

SolveF = ma2000 N = (1000kg) a2000N = (1000kg) a1000kg = 1000kg

2 m/s2 = a

Class work

• Please complete #3-7 on page 65 in the textbook

Closing

TopicSuppose a cart is being

moved by a force. If suddenly a load is dumped into the cart so that the cart's mass increases, what happens to the cart's acceleration?

WHY?

Facts

Homework

DUE NEXT CLASS• Read chapter 4 for review of the 2nd law