Newton's Laws of Motion
IMAT Interactive Study Tool
Newton's First Law: The Law of Inertia
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
This is the concept of inertia - an object's resistance to a change in its state of motion. If the net force on an object is zero, its velocity is constant.
If \(\sum F = 0\), then \(a = 0\).
Newton's Second Law: Force and Acceleration
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
\(\sum F = ma\)
Interactive Demo: F = ma
Newton's Third Law: Action-Reaction
For every action, there is an equal and opposite reaction. If object A exerts a force on object B, then object B simultaneously exerts an equal and opposite force on object A.
\(F_{A \text{ on } B} = -F_{B \text{ on } A}\)
Crucial Misconception: The action and reaction forces always act on different objects. They never cancel each other out.
Embedded PhET Simulation
Use the interactive simulation below to explore the concepts of force, mass, acceleration, and friction. Try applying different forces to objects of different masses and observe the results.
1. True or False: If an object is moving, there must be a net force acting on it.
Example 1: Finding Net Force
A 5 kg block is pushed to the right with a force of 40 N. A frictional force of 15 N opposes the motion. What is the block's acceleration?
Step 1: Calculate the net force (\(\sum F\)).
The forces are in opposite directions. Let's define "right" as the positive direction.
\(\sum F = F_{push} - F_{friction} = 40 \, N - 15 \, N = 25 \, N\)
Step 2: Use Newton's Second Law to find acceleration.
\(a = \frac{\sum F}{m} = \frac{25 \, N}{5 \, kg} = 5 \, m/s^2\)
Conclusion: The block accelerates to the right at 5 m/s².