The law
What does Newton's first law say about an object at rest.
It says at rest unless an unbalanced external force acts on it.
What is inertia
An object's tendency to resist changes in its motion.
A soccer ball rests on the grass. What must happen for it to move?
An external, unbalanced force.
What does the law say about an object in motion?
It keeps moving at constant speed in a straight line unless acted on by an unbalanced force.
Which has more inertia: an empty cart or a full cart
the full cart because it has more mass.
Why does a book stay still on a desk?
The forces on it are balanced, so its motion does not change.
What is another name for Newton's first law?
The law of Inertia
What property of an object affects its inertia?
Its mass.
A hockey puck slides on nearly frictionless ice. What would it do?
Keep moving in a straight line at a constant speed until a force changes its motion.
what kind of force changes an object's motion?
An unbalanced force.
When a car stops suddenly, why do passengers move forward?
Their bodies tend to keep moving because of inertia.
What force usually slows a rolling ball down?
Friction.
Complete the idea: motion does not change unless....
An unbalanced external force acts on the object.
True or false: objects with greater mass gave greater inertia.
true.
A seat belt helps protect you when a car stops quickly. What law explains why it is needed?
Newton's first law of motion: your body tends to keep moving due to inertia.