Motion and Force

A.  Motion

1.  Motion is a change in position.

2.  Reference points are necessary to determine motion.

B.  Speed

1.  Speed is the rate of change in position.

2.  Types of speed:

a.  Instantaneous speed - the rate of motion at any given moment.

b.  Constant speed - speed that does not vary.

c.  Average speed - total distance traveled divided by total time of travel.

3.  Speed formula:  speed = distance / time (or v = d / t)

C.  Velocity

1.  Velocity is speed in a defined direction.

2.  Velocity can change even if speed is constant as long as the direction changes.

D.  Acceleration

1.  Acceleration is the rate of change of velocity.

2.  Acceleration formula:  acceleration = change in velocity / time (or a = [v(f)-v(i)] / t)

3.  Acceleration can be a large amount if either the change in velocity is large or if it occurs fast.

4.  Negative acceleration is usually called deceleration.

5.  Units are meters per second per second (or meters per second^2)

E.  Force and Motion

1.  A force is a push or a pull one body exerts on another body.

2.  Balanced forces

a.  Forces that are equal in size and opposite in direction.

b.  Do not result in a change in velocity (a balaced tug of war).

3.  Unbalanced forces

a.  Forces are not equal.

b.  Result in a net force.

c.  Causes an object to change velocity.

F.  Inertia

1.  Inertia is the tendency of an object to resist any change in its motion.

2.  Inertia is directly proportional to mass (greater mass means more inertia).

G.  Newton's 1st Law of Motion

1.  Objects in motion tend to remain in motion at the same velocity and objects at rest tend to remain at rest unless acted upon by an unbalanced force.

2.  Also called the Law of Inertia.

3.  Simply put:  objects resist changes in their state of motion.

H.  Friction

1.  Friction is a force that opposes motion between two surfaces that are touching each other.

2.  Industry generally tries to reduce the friction between moving parts using lubricants.

3.  Friction is necessary for life because we depend on it to hold things together.

I.  Gravity

1.  The force of gravity is an attractive force between objects.

2.  The amount of gravitational force between objects depends upon their:

a.  Masses (greater mass means more gravity)

b.  Distance apart (greater distance means less gravity)

3.  Weight is the force of gravity between the earth and a body on its surface.

a.  Weight is NOT the same as mass!

b.  Weight is measured in newtons (N).

4.  Gravity itself is measured as acceleration (9.8 m/s/s on the earth).