6.1 Force changes motion A force is a push or pull, or any action that is able to change motion.

6.1 Law of inertia Newton’s first law says that objects continue the motion they already have unless they are acted on by a net force. If the net force is zero, an object at rest will stay at rest. If an object is acted upon by unbalanced forces, its motion will change.

According to these vectors, in what direction is the net force? Newton’s first law is often written in terms of the net force: “An object at rest will stay at rest and an object in motion will continue in motion at constant velocity UNLESS there is a net force.” According to these vectors, in what direction is the net force?

6.1 Law of inertia Inertia is the property of an object that resists changes in motion. Objects with more mass have more inertia and are more resistant to changes in their motion. Which ball has more inertia?

6.2 Newton’s second law Newton’s first law tells us that motion cannot change without a net force. According to Newton’s second law, the amount of acceleration depends on both the force and the mass.

6.2 The newton The S.I. unit of force (newton) is defined by the second law. A newton is the amount of force needed to accelerate a 1 kg object by 1m/s.

6.2 Newton’s second law There are three main ideas related to Newton’s Second Law: Acceleration is the result of unbalanced forces. A larger force makes a proportionally larger acceleration. Acceleration is inversely proportional to mass.

6.2 Newton’s second law Unbalanced forces cause changes in speed, direction, or both.

6.2 Acceleration and force The second law says that acceleration is proportional to force. If force is increased or decreased, acceleration will be increased or decreased by the same factor.

6.2 Acceleration and direction Another important factor of the second law is that the acceleration is always in the same direction as the net force.

6.2 Acceleration and mass The greater the mass, the smaller the acceleration for a given force. This means acceleration is inversely proportional to mass.

6.2 Acceleration, force and mass The acceleration caused by a force is proportional to force and inversely proportional to mass.

The stronger the force on an object, the greater its acceleration. Force is directly proportional to acceleration. If twice the force is applied, the acceleration is twice as great.

The greater the mass, the smaller the acceleration for a given force. Mass is inversely related to force. An object with twice the mass will have half the acceleration if the same force is applied.

6.3 Newton’s Third Law Newton’s Third Law (action- reaction) applies when a force is placed on any object, such as a basketball.

6.3 The Third Law: Action/Reaction Newton’s Third Law states that every action force creates a reaction force that is equal in strength and opposite in direction. There can never be a single force, alone, without its action-reaction partner.

6.3 Action and reaction When sorting out action and reaction forces it is helpful to examine or draw diagrams. Here the action force is on the ________________, and the reaction force is on the _______________.

6.3 Collisions Newton’s third law tells us that any time two objects hit each other, they exert equal and opposite forces on each other. The effect of the force is not always the same.

6.3 Collisions When a large truck hits a small car, the forces are equal. The small car experiences a much greater change in velocity much more rapidly than the big truck. Which vehicle ends up with more damage?