Mass, Force and Motion

8th Grade Physical Science

S8P3. Students will investigate the relationship between force,

mass, and the motion of objects.

b.Demonstrate the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction.

What is a force?

Calculating Net ForcesA net force is the total amount

of all forces acting on an object.

Add forces moving in the same direction.

Subtract forces moving in opposite directions.

BALANCED FORCES vs. UNBALANCED FORCES

• Balanced forces are always equal to ZERO and DO NOT cause motion.

• Unbalanced forces ALWAYS cause motion and NEVER equal to zero.

FRICTION is a force that works in the opposite direction to motion.

Static Friction vs. Kinetic Friction• Static friction is found

where there is NO motion.

• Kinetic friction is found where MOTION occurs.

Newton’s 1st Law of Motion

Newton’s 1st Law of Motion or The Law of Inertia states…..

An object at rest tends to stay at rest and an object in motion tends

to stay in motion unless an unbalanced force acts upon it.

Newton’s 2nd Law of Motion

More on the Law of Acceleration

Newton’s 3nd Law of Motion

According to Newton’s 3rd Law of Motion, Forces Always Come In Pairs (or Twos)

SI (International System) Units of Measurement

We measure forces in NEWTONS.We measure weight in NEWTONS.

Weight is measurement of the FORCE of GRAVITY.

Gravity is a major force in the universe!

S8P5. Students will recognize the characteristics of gravity,

electricity, and magnetism as major kinds of forces acting in

nature.a. Recognize that every object exerts gravitational force on every other object and that the force exerted depends on how much mass the objects have and how far apart they are.

Gravitational Force

The Force of Gravity and Mass

The Force of Gravity and Distance

S8P3. Students will investigate the relationship between force,

mass, and the motion of objects.

a. Determine the relationship between velocity and acceleration.

Speed and Velocity

Velocity has a direction…..Speed does not go in a particular direction.

Both use the same equation:Speed or Velocity = distance time

Velocity and Acceleration

SI (International System) Units of MeasurementWe measure speed in m/s.

We measure velocity in m/s.We measure acceleration in m/s2.

(Or…meters per second per second.)

S8P3. Students will investigate the relationship between force,

mass, and the motion of objects.

c. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw, and wheel and axle) on work.