懂你英语流利说Level4－Unit1 2/4 Vocabulary

A force is push or pull on a object.

A force changes the motion of a moving object.

A force can be strong or weak and is always has direction.

The earth is a planet that goes around the sun in a circular orbit

This speed of motion doesn't change,but direction of motion does.

The earth has a layer of gas above its surface which helps to support life

Atoms are the building blacs of matter.

At the center of an atom is its nucleus,which has a positive electric charge

Outside the nucleus are electron which have negative charge

Asteroids that pass closed to the Earth are called near-earth objects.

Without an atmosphere,there would be no life on Earth.

If they colide with Earth they could cause an extinction event.

A rectangle is a two dimensional figure with 4 sides.

The two lines on the left intersect each other at a right angle,which is 90 degrees.

The two lines on the right are parallel which means they never cross.

The earth is a planet that goes around the sun in a circular orbit.

All points on the surface of a sphere are equidistant from its center

The opposite sides of a rectangle are equal and parallel,which means they never cross.

The area of a rectangle is the length times the width

A force can increase or decrease the speed of an object,and it can change the direction of motion