NEWTON'S LAWS

NEWTON'S FIRST LAW

• Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

NEWTON'S THIRD LAW

• Whenever one body exerts a force on another, the second always exerts on the first a force which is equal in absolute magnitude, opposite in direction, and has the same line of action.

• Note: Action-reaction forces act on different bodies

NEWTON'S SECOND LAW: Fnet = ma

• If there is an unbalanced force on an object, we find that the VELOCITY of the object changes. There is an acceleration.
• We find that Fnet , the unbalanced force, is proportional to the acceleration, a
• The proportionality factor is the mass, m.
• Fnet = ma
• Here Fnet is the vector sum of all forces acting on the object.
• The units are [lbs] = [slugs][f/s2] or [newtons] = [kg][m/s2]

MASS AND WEIGHT

• The weight of an object is the force of attraction between the earth and the object
• Weight is proportional to the acceleration of gravity
• W = mg
• Since the acceleration of gravity may be different for different planets, weight may be different for different locations. However, for a given object the rest mass is constant.