# Newton's first law of motion

### Newton's first law of motion

#### Lessons

In this lesson, we will learn:
• Newton's first law of motion
• Inertia
• Explaining physical phenomena using Newton's first law and inertia

Notes:

• Newton's first law of motion can be stated as "if no net force acts on an object, then the velocity of the object does not change."
• Net force is a vector sum of forces acting on an object.
• Newton's first law is also called the law of inertia. Inertia is an idea that originated from Galileo, which says that objects have a tendency to resist changes in their motion:
• Objects in motion will tend to stay in motion by continuing at their velocity in a straight line, and objects at rest tend to stay at rest.
• Objects with more mass have "more inertia". It is more difficult to get a more massive object change its velocity by speeding up, slowing down, or changing direction.
• Introduction
Introduction to Newton's first law
a)
What is Newton's first law?

b)
What is inertia?

• 1.

Explain physical observations using Newton's first law and inertia

Explain using Newton's $1^{st}$ Law or inertia:

a)
True or false: a vase sitting still on a desk has no horizontal forces acting on it. Explain your answer.

b)
Why do you press against your seatbelt when you are in a car that stops suddenly?

c)
A shopping cart is pushed at a constant velocity of 1.5 m/s with a force of 40 N. What is the net force acting on the cart?