lineeye2.gif Section 1

1. Newton's 1st Law ( a.k.a The Law of Inertia):
A body at rest will remain at rest, and a body in motion will remain in motion at a constant speed in a straight line, unless it is acted on by a net, external force.

2. Inertia: The resistance to change in motion.
The mass of a body is a measure of its inertia.

lineeye2.gifSection 2

1.Newton's 3rd Law:
For every action (force) there is an equal and opposite reaction (force).

Here are some key points we learned about this law.

2. Forces occur in matched pairs. We call the instigator of the interaction the action force. The force that responds is called the reaction force. Note that there are two forces, exerted by two bodies on each other.

3. Action-Reaction forces act in opposite directions.

4. Even inanimate objects can exert forces.

5. Forces do not require contact. Many forces, such as gravity act at a measureable distance.

lineeye2.gifSection 3

1. For zero net force, a force vs. time graph would be a straight, horizontal line at F = 0.
A velocity vs. time graph will be a straight, horizontal line. The height of the graph would be equal to the constant velocity.

2. If there is a non-zero net force, a force graph should again be a horizontal line, but this time it will indicate a non-zero force.

3. A constant (net) force produces a constant acceleration.

4. The weight of an object is not a property of the body. It is a force that acts on it and it is not constant. If you move it to the moon it will weigh less than it does on the earth.

5. The mass, however, is a property of a body and it will be the same everywhere.

6. Newton's 2nd Law:
The acceleration of a body is directly proportional to the net force acting on it and inversely proportional to the mass of the body.

lineeye2.gifSection 4

1. Newton's 2nd Law, , is a vector equation. This means that the direction of each side is the same. The direction of the net force is found by vectorially adding the forces.

2. To help us visualize and identify all important forces, we draw a free-body diagram, FBD. In a FBD, we draw a dot which represents the object under study. Each force acting on it is represented as a scaled arrow radiating outward.

lineeye2.gifSection 5

1. In solving problems using the 2nd law, we start by drawing a FBD showing all forces acting on the body. We then write , where Σ²F is the vector sum of all the forces. We can then solve this equation for any variable we need.

lineeye2.gifSection 6

1. Weight is directly proportional to mass.

Weight = mass x g
g = 9.8 N/kg

2. The "g" in W = mg is about 9.8 N/kg everywhere on earth. On other bodies in the universe it has different values.

lineeye2.gifSection 7

1. When a body accelerates in a vertical plane, its weight is one of the forces that makes up the net force on it. For a body to have a vertical acceleration other than "g", it must have some other force acting. We sometimes refer to this other force as the apparent weight.

Apparent Weight: The support force on a body while it's accelerating up or down.