Ch 11 Lesson 2--Forces and Motion

force

Any push or pull from one object to another. Example: The __ made the cart start moving.

newton

A unit used to measure force. Example: The scale read 4 __ when I pulled the spring.

force diagram

A drawing that shows forces with arrows. Example: We drew a __ to explain the tug-of-war.

arrow

A symbol that shows direction and size on a diagram. Example: A longer __ showed a stronger push.

strength

How large a force is. Example: The bigger __ of the pull moved the box farther.

contact force

A force that happens when objects touch. Example: The __ happened when my hand pushed the door.

noncontact force

A force that acts without touching. Example: A __ pulled the paper clip toward the magnet.

thrust

A force that pushes or pulls something forward. Example: The engine’s __ sent the plane down the runway.

lift

A force that raises an airplane into the air. Example: Strong __ helped the airplane rise smoothly.

weight

The downward pull of gravity on an object. Example: The backpack’s __ made my shoulders tired.

drag

A pulling force that slows motion through air. Example: The parachute increased __ and slowed the fall.

friction

A force that opposes motion between surfaces. Example: __ made the scooter slow on the rough path.

air resistance

A force from air that slows moving objects. Example: More __ made the falling leaf drift longer.

balanced forces

Forces that add up to zero and do not change motion. Example: With __, the book stayed still.

unbalanced force

A force that causes motion to change. Example: An __ made the wagon speed up fast.

total force

The sum of all forces acting on an object. Example: The __ was not zero, so it accelerated.

action force

The push or pull of one object on another. Example: The __ happened when I pushed the wall.

reaction force

The equal-strength push or pull back. Example: The __ pushed me upward when I jumped.

free fall

Falling while gravity is the main force acting. Example: In __, the rider felt almost weightless.

shape

The form of an object. Example: The clay changed __ when I pressed it flat.