Lesson 8: Newton's First Law

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.​

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​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.

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.

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​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.

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.​

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

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

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

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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 states, if the net force on an object is zero, then the motion of the object does not change.

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​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.

​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.