Chapter 5 Force
Kinematics study of how objects move
Dynamics study of why objects move as they do
5.1 Newtons Laws of Motion
Force a push or pull
Four types of Forces
- gravitational force
- electromagnetic force
- strong nuclear force
- weak force
Newtons First Law of Motion
An object with no force acting on it moves with constant velocity.
An object with no net force acting on it remains at rest or moves with constant velocity in a straight line.
Newton Second Law of Motion
The acceleration of a body is directly proportional to the net force on it and inversely proportional to its mass.
a = F/m or F = ma
The Unit of Force
F = ma = (1.00 kg)(1.00 m/s^2) = 1.00 N (Newton)
Newtons Third Law of Motion
When on object exerts a force on a second object, the second exerts a force on the first that is equal in magnitude but opposite in direction.
5.2 Using Newtons Laws
Mass and Weight
Weight - the gravitational attraction of a large body, usually Earth.
W = mg
Two Kinds of Mass
Inertial mass
M = F/a
Gravitational Mass
a. use a balance
b. can not be measured in zero gravity
Friction force that opposes the motion between two surfaces that are in contact
Types of Friction
a. fluid
b. rolling
c. static
d. sliding
F(f) = uF(n)
u(mu) coefficient of friction (depends on the two surfaces in contact)
Friction acts in a direction parallel to surfaces in contact and opposes the motion.
Problem Solving Strategy
- Always sketch a neat drawing of the object.
- Draw arrows representing all the forces action on the object.
- Label each force with the cause of the force.
The Net Force Causes Acceleration
The Fall of Bodies in the Air
An object in freefall (in a vacuum) has only the force of gravity acting on it. Its acceleration equal to g.
The force of air molecules striking a moving object is called air resistance.
Terminal velocity the constant velocity of a body free falling when the air resistance equals its weight.
