Forces

I. California Standards

8.1.e Students know changes in velocity may be due to changes in speed, direction, or both.

8.2.e Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).

8.2.a Students know a force has both direction and magnitude.

I. California Standards

8.2.b Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.

8.2.c Students know when the forces on an object are balanced, the motion of the object does not change.

8.2.d Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction.

II. Definitions

A. A force is anything that causes acceleration.1. Is a push or a pull2. Has a direction and magnitude

B. Acceleration is a change in speed, direction, or both.

C. Magnitude is size or strength.

III. Examples

A. GravityB. Magnetic ForceC. Friction

1. Static Friction2. Rolling Friction3. Air resistance

III. Examples

D. Elastic Forces1. Tension2. Compression

E. Nuclear ForcesWhat forces are

acting on your stool right now?

What forces are acting on this box

on the hill?

IV. Representing Force

A. An arrow shows the direction of the force.

B. The length of the arrow or a measurement by the arrow represents the force’s magnitude.

V. Measuring Force

A. Units1. Newtons (1 pound = 4.4 N)2. Gs (1g = the force of Earth’s

gravity at the surface)3. Pounds (lbs) 4. Pounds per square inch (psi)

How much force does gravity exert

on you?

V. Measuring Force

A. Tools1. Scale 2. Spring Scale3. Pressure Gauge4. Barrometer

Use your spring scale to measure the force gravity

exerts on the weights.

VII. Net Force

A. Net force is the combined effect of all forces acting on an object.

B. If the forces work in the same direction, add them together.

What is the net force?

VII. Net Force

C. If the forces go in opposite directions, subtract them.

What is the net force?

VII. Net Force

A. If the net force is 0, the forces are balanced, and there will be no change in motion.

B. If the net force is not 0, the forces are unbalanced, and motion will change in the direction of the net force.

VII. Net ForceWill the box move? Why?

VII. Net ForceForce to the Left Force to the Right Are the forces

balanced?Describe the Motion