 # Chapter 12 Review FORCES.

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Chapter 12 Review FORCES

FORCE A PUSH OR A PULL

CONTACT FORCE A FORCE THAT IS EXERTED ONLY WHEN TWO OBJECTS ARE TOUCHING.

CONTACT FORCE A force that is applied only when two objects are touching.

NONCONTACT FORCE A FORCE THAT ONE OBJECT EXERTS ON ANOTHER WHEN THEY ARE NOT TOUCHING. Noncontact forces include the gravitational force, electric force, magnetic force.

It is the non contact force of gravity that keeps the Moon revolving around the Earth and all of the planets revolving around the Sun.

Force is a vector Force is a vector because it has size and direction. The direction is usually represented by an arrow. The unit for the size of a force is the newton (N).

NET FORCE THE COMBINATION OF ALL FORCES ACTING ON AN OBJECT IS CALLED THE NET FORCE N -100 N +

BALANCED FORCES When the forces acting on an object are balanced, the motion of an object does not change. Question: Can the object be moving even when the forces are balanced? + 100 N N Net Force Equals 0 Newtons

BALANCED FORCES When the forces on an object are balanced, the motion of the object does not change. When the force of gravity acting down on a boat is equal to the buoyant force acting up on a boat, the forces are balanced and the boat floats.

When the upward force of air resistance is equal to the downward pull of gravity, the forces become balanced.

UNBALANCED FORCES When the net force on an object is not zero, the forces are unbalanced and the object is in motion. 100 N + 25 N push friction

Unbalanced forces cause an object or objects to move.

weight Weight is the gravitational force exerted on an object. A bathroom scale measures the force of the gravitational attraction between you and the earth.

friction A force that opposes the movement between two surfaces in contact.

Sliding (Kinetic) Friction

Static friction

gravity An attractive force that exists between all objects that have mass. Our atmosphere is a result of earth’s gravitational force.

elastic force The force exerted by a material when it is stretched or
compressed. The diving board applies an upward elastic force when it is bent downward by the diver.

tension force A tension force is a pulling force applied to an object that can make the object stretch. The force applied to a rubber band when stretching it is this type of force.

compression force A compression force is a squeezing force applied to an object that can make the object shrink.

Normal Force

Newton’s 1st Law of Motion
An object in motion tends to stay in motion, and an object at rest tends to stay at rest unless the object is acted upon by an outside force.