A force is the push or a pull on the object. A force changes the motion of a moving object.
A force can be strong or weak and it always has a direction.
The earth is a planet that goes around the sun in the circular orbit. The speed of its motion doesn’t change and the direction of its motion does. The earth has a layer of gas above its surface, which helps to support life.
Atoms are the building blocks of matter. At the center of an atom is its nucleus, which has a positive electric charge. Outside the nucleus are electrons, which have a negative charge.
Asteroids and comics are object that orbits our sun, but are smaller than planets. Asteroid that pass close to the earth are called the near-earth objects. The layer of gases, just above the earth surface, is our atmosphere. The atmosphere is made up of gases, such as oxygen and hydrogen. Without an atmosphere, there will be not life on the earth.
Asteroid? n.[天]小行星;海盤(pán)車(chē);海星? adj.星狀的
orbit? n.軌道;眼眶;勢(shì)力范圍;（人生的）旅程概荷，生活過(guò)程
vt.& vi.在…軌道上運(yùn)行遏乔，環(huán)繞軌道運(yùn)行
vi.盤(pán)旋;繞軌道運(yùn)行
vt.繞軌道而行;進(jìn)入軌道
The two lines on the left intersect each other at a right angle which is 90 degrees. The 2 lines on the right are parallel, which means they never cross.
The adjacent sides of rectangle are perpendicular, which means they meet at a 90-degree angle. The opposite sides of the rectangle are equal a parallel, which means they never cross. The area of a rectangle is the length times the width.
Intersect? ? ? vt.橫斷稿存，橫切赁炎，橫穿? ? vt.& vi.（指線條妇穴、道路等）相交犬性，交叉
A circle is the 2 dimensional figures with radius and circumference which is the distance around the circle. The area of the circle is π R square, where r is the radius and Pi is the ratio of the circle’s circumference to its diameter.
Radius n.橈骨;半徑范圍;半徑（距離）;用半徑度量的圓形面積
Dimensional adj.維的;尺寸的;<物>量綱的;<數(shù)>因次的
A sphere is a 3 dimensional figure with the a ratio and volume, which is the three-fourth πR cube. All points on the surface of the sphere are equidistance from its center.
Cube? ? n.立方形，立方體;立方碎浇，三次冪;小房間
vt.求…的立方;把（食物）切成小方塊;測(cè)定…的體積
equidistance 等距離的
A right triangle is a 2 dimensional figure with 3 sides, 2 of which are perpendicular. To find its area, multiply the length of the 2 perpendicular sides, A and B and divided by 2, A equates one half A B.
Perpendicular
adj.垂直的临谱，成直角的;直立的咆畏，險(xiǎn)陡的;[建]垂直式的;〈謔〉直站著的
n.垂直線，垂直面;直立吴裤，直立姿勢(shì)，廉直;垂直測(cè)器溺健，錘規(guī);[建]垂直式建筑麦牺，絕壁
Equate? vt.等同;使相等;相當(dāng)于
the electric force between the nucleus and the electrons holds the atom together.
A force can increase or decrease the speed of an object, and it can change the direction of motion.
