F2 Forces – Fill in the blanks

The unit of force is the _______________ newton【牛頓】 and it can be measured by a _______________ newton balance【牛頓秤】 or a _______________ spring balance【弹簧秤】.

A force can change the _______________ speed, the _______________ direction of motion and the _______________ shape of an object.

Catching a football changes it’s _______________ speed. Striking a volleyball changes its _______________ speed and _______________ direction of motion. Pressing on a inflated balloon【充氣氣球】 changes its _______________ shape.

When an object applies【施加】 a force on another objects through direct contact, the force is called a _______________ contact force while an object applies a force on another object that is not in direct contact, the force is called a _______________ non-contact force.

Place two bar magnets on a bench with opposite poles【相反的兩極】 facing each other, then move one magnet slowly towards the other. We will see the magnets _______________ attract【吸引】 each other.

Place two bar magnets on a bench with same poles【相同的兩極】 facing each other, then move one magnet slowly towards the other. We will see the magnets _______________ repel【排斥】 each other.

_______________ Magnetic force and _______________ the force of gravity【重力】 are examples of non-contact force.

When an object slides【滑動】 over another object, a force arises【出現】 to oppose【抵抗】 this change. We call this force _______________ friction【摩擦力】.

Friction is a _______________ contact force between two contacting surfaces【接觸表面】 that slide【滑動】 on each other. It always _______________ opposes【抵抗】 the motion of an object.

The _______________ faster an object moves in water or air, the _______________ greater the opposing force acting on it. The opposing force acting on an object by air is called the _______________ air resistance【空氣阻力】.

When an object moves against friction【抵抗摩擦】, its _______________ kinetic energy changes to _______________ heat energy. This energy conversion is often unnecessary and leads to【引致】 a waste of energy. Therefore, different ways have been found to _______________ reduce friction to _______________ save energy.

For an object moving in air or water, the resistance【阻力】 can be reduced【降低】 by making the object _______________ streamlined【流線型】 in shape.

The weight of an object on Earth is _______________ the force of gravity【重力】 acting on the object by the Earth. It is measured in _______________ newtons. The mass of an object shows the _______________ amount of matter【物質量】 in the object. It is measured in _______________ kilograms or _______________ grams.