The Nature of Force

Newton’s Laws

What is a Force?

• A force is a push or a pull. • When one object pushes or

pulls another object, you say that the first object is exerting a force on the second object.

• Forces are described not only by how strong they are, but also by the direction in which they act.

Forces

• In order to create motion (or stop it ) you must have an unbalanced force.

• Balanced forces cancel each other out. (No motion)

• When two forces act in the same direction they add together. (creating an unbalanced force)

• When forces act in opposite directions, an one is larger than the other, the overall force is in the direction of the greater force.

Newton’s Laws

• Isaac Newton was an English mathematician who discovered the three basic laws of motion.

• His first law: – An object at rest will stay at rest, and an object

in motion will stay in motion unless acted on by an unbalanced force. AKA: Law of Inertia

Inertia: the tendency of an object to resist change in its motion.

Newton’s First Law

• The amount of inertia an object has, depends on its mass.

• The greater the mass, the greater its inertia.

                                                               

                            

A lot of inertia! Very little inertia

Newton’s Second Law

• Newton’s second law of motion states that The net force on an object is a product of its acceleration and its mass.

• Or, an easier way to remember this is:

F =Mass x Acceleration

Newton’s Second Law

• F = M*A

Mass = 5 kg

Let’s assume that the wheels of a 5-kg car apply 10 N of force. The net force would equal 10 Newtons.

What is the acceleration of the car?

Newton’s Third Law

• Newton’s third law states that: For every action, there is an equal and opposite reaction.

Action-Reaction

Recap!

• 1. An object in motion will stay in motion, or an object at rest will stay at rest unless acted on by an unbalanced force.

• 2. Force = Mass x Acceleration

• 3. For every action, there is an equal and opposite reaction.