Lesson 8: Newton's First Law

Lesson 8: Newton's First Law

An object in motion...

​Identifying Forces

Identifying forces allows us to figure out what different forces are in play and what each force is doing when we observe a specific action.​

​

​The image to the right shows "pull" forces. If the force of the guy on the right is greater than the force against him from the guy on the left, then he will pull the other guy towards him.

​Identifying Forces

The combination of all the forces acting on an object is the net force. In the image to the right, the net force is greater with each person moving in the same direction.

​

​In the bottom image, the two forces push against each other and are subtracted from each other. The guy with the greater force pushes the block towards the other guy.

Net Force

If multiple forces move in the same direction, their strengths are added together. If multiple forces move in opposite directions, their forces are subtracted and the greater force moves the object in its direction.​

​Balanced and Unbalanced Forces

​If forces moving in opposite directions are equal, then the forces are balanced and there is no movement of the object.

​

​If forces moving in opposite directions are not equal, then the forces are unbalanced and the object moves.

​Balanced and Unbalanced Forces

​So, balanced forces are forces acting on an object that combine and form a net force of zero.

​

Unbalanced forces are forces acting on an object that combine and form a net force that is not zero.

​Newton's First Law of Motion

​Newton's First Law of Motion states, if the net force on an object is zero, then the motion of the object does not change.

​

​This means an object at rest stays at rest if it isn't acted on by an outside force. And an object in motion stays in motion unless acted on by an outside force.

​Inertia

​The tendency of an object to resist a change in its motion is called inertia. This is observable in

​the jerking feeling you get

​when a car stops quickly

​because the car stops, but

​your body tries to keep going.

Multiple Choice

True or False:

Balanced forces cause an object to change its motion.

• True

• False

Multiple Choice

_________________ is an object's tendency to resist a change in motion.

• inertia

• malleability

• net force

• balanced forces

Multiple Choice

If two people push a dresser in the same direction, one at 50 newtons and the other with a force of 100 newtons, how much net force is acting on the dresser?

• 150 N

• 50 N

• 200 N

• 100 N