Force and Motion Notes

Motion

What is motion? / A change in the position of an object with respect to time
How do you know something has moved? / Establish a reference point
What causes an object to move? / A force acting upon the object
What is a force? / A push or a pull
Can more than one force act on an object at the same time? / Yes!

Balanced Forces

•A balanced force is one in which the net force ______equals 0______.

•Is there any motion? No

•Examples:A tug-of-war contest in which both sides are of equal strength

Unbalanced Forces

•An unbalanced force is one in which the net force is ___greater than 0__.

•Is there any motion?Yes

•Examples:A tug-of-war contest when one side is stronger than the other.

•Only an __unbalanced______force can change the motion of an object.

•What would happen if an unbalanced force acted on an object that’s already in motion?

It changes the speed or direction of an object

Unbalanced forces can act in the ____same______direction.

•Example: Two people are pushing and pulling a cabinet to move it. One person is pushing with a force of 20N and the other is pulling with a force of 20 N.

•How do you get the NET FORCE?20N + 20N= 40N

•What direction does the object move?Same direction as each of the two forces

Unbalanced forces can act in ___opposite______directions.

•Example: Two dogs are tugging on a toy. One is pulling with a force of 15 N while the other is pulling with a force of 10N.

•How do you get the NET FORCE?15N- 10N= 5N

•What direction does the object move?In the direction of the stronger dog.

Mass and Inertia

Newton’s 1st Law: The Law of Inertia

•What does it say?An object in motion tends to stay in motion, while an object at rest tends to stay at rest unless an unbalanced force acts upon them.

Inertia

•What is it?Tendency of an object to resist a change in motion.

•Example: A car going 50km/h comes to a sudden stop. The people inside will continue to move forward unless a force prevents them from going through the windshield.

Mass

•The mass of an object affects its’ __inertia______.

•Objects with more mass have ___more______inertia than an object with a smaller mass.

•Examples:Pulling a wagon full of rocks will be harder than pulling an empty wagon

Friction and Gravity

What is friction? A force that opposes the motion of an object
When does it occur? When an object in motion rubs against a surface
What happens to the object when friction acts on it? It reduces the speed of the object
What affects the amount of friction? The push or pull on the object, the bumpiness of the surface, and the weight of the object being pushed.
What is gravity? The force of attraction between all objects
The amount of gravity depends on two things: The mass of the objects and the distance between them
Examples: When someone throws a ball, it will eventually hit the ground unless someone catches it.