acceleration: a change in the (speed, direction, or both) of a body

When any moving object goes , it is accelerating.

atmosphere: the that surround a planet

These layers include ozone layer that protects us from .

Greek roots: atmos meaning " , steam"; sphaira meaning "globe, ball"

contact: the act of

An electrical needs to have contact between the wires, battery, and light bulb. The contact allows electricity to flow.

Earth: the planet from the Sun

Earth is the only place in the solar system that has everything we need to live - air, water, and comfortable .

force: a that is applied to an object

Fill up a balloon with air and then let it go. The air in the balloon quickly escapes and the balloon moves in the opposite direction. This is caused by the force of the air.

frame of reference: an item against which the of an object can be measured

A person standing at a bus stop sees the of a car differently than the car’s passengers see the same motion.

friction: a force that the motion of a body across a surface or through a gas or liquid

It is easier to walk on a dry surface than it is to walk on ice. You keep slipping on ice because ice has friction

kinetic energy: the energy an object has due to its

An object's kinetic energy is one half the product of the object's and the square of its .

Greek root kinetikos meaning " , putting in motion" Greek root energos meaning " "

kinetic friction: a force between two objects moving pass each other

Objects that appear smooth are actually quite when you examine them on a microscopic level, making it difficult for two objects to slide past each other.

Greek root kinetikos meaning "moving, putting in motion"

magnitude: size of ground movement caused by due to energy released

During an earthquake, magnitude is measured on a logarithmic scale called the scale.

mass: the amount of in an object

A penny has a mass of about grams. A big book may have a mass of grams. It is much harder to toss a book than a penny. The book has more mass.

Newton's laws: the three laws Isaac Newton discovered governing the motion of objects

Newton's first law states: "An object in motion , unless acted on by a force. An object at rest stays at rest unless acted on by a force."

Newton's second law states: "Force is the product of ."

Newton's third law states: "For every action force, there is an reaction force."

orbit: the of an object as it revolves around another object

Earth and the other planets in the solar system go around the Sun in .

potential energy: the amount of energy that is in an object; energy that an object has because of its position relative to other objects

When you stretch a rubber band, it’s ready to spring back. You’ve added potential energy to it. This energy might do something. But it isn’t doing anything yet. Once you let go, you release the .

speed: traveled per unit of time

Speed is a measurement of an object is moving. A slow-moving object covers a small amount of distance in the same unit of time. An object with no movement or at rest has a zero speed.

surface: the of an object; the outside of an object; the boundary between two objects or materials

All objects have surfaces.

velocity: the speed and of moving objects

Speed is how fast something is traveling. Velocity is both the speed of the object and the in which it is traveling.

weight: the force of on an object

Earth’s pulls everything toward its center. We call this pull weight.

work: a force applied to an object over a

How do you make a bicycle work? You need to get on the bicycle and use your legs to pedal. You transfer the energy in your leg muscles to mechanical energy through the pedals of the bicycle. The bicycle begins to move. You can move faster by working your muscles to transfer more energy and pedal faster. Work is the result of that makes things happen.