Unit 2
Activity 1: What are the phenomena of force?
1. In everyday life, we often see various force phenomena. Some forces can change an object’s shape; some can change an object’s state of motion. Examples: pressing clay with both hands, pulling a rubber band with both hands, kicking a ball with your foot.
2. The magnitude, direction, and point of application of a force affect how it acts on an object; these are called the three elements of force. When applying a force, the location where the object is touched is called the point of application. Use the length of a line segment to represent the magnitude of the force, and use an arrow to indicate the direction of the force.
Activity 2: What are the properties of magnetic force?
1. Magnets have magnetic force and can attract iron objects.
1-1. Can be attracted by a magnet: binder clips, paper clips, staples, scissors (blade area)
1-2. Cannot be attracted by a magnet: colored paper, markers, erasers, tape, pencils, ten-dollar coin.
2. The strength of magnetic force varies at different parts of a bar magnet; typically, the force is stronger at both ends, called the magnetic poles, which are the N pole and S pole.
3. The strength of magnetic force is not necessarily related to the size of the magnet. You can compare the strength by the number of paper clips it can attract. The stronger the magnet, the more paper clips it can attract.
4. When the magnetic poles (N and S) of magnets approach each other, like poles repel and unlike poles attract.
5. Using a magnet’s ability to attract iron and to act through barriers, you can quickly and conveniently separate iron filings from sand on the ground.
6. In daily life, magnets are often used to attract iron items or to fix objects using the attraction between opposite poles.
7. Adding iron plates on both sides of a magnet can increase its attraction. For example, on items like pencil cases or door stoppers, you can find two iron plates added next to the magnet.
Activity 3: What other kinds of forces are there?
1. There are other types of forces used in life, such as elastic force, wind force, and buoyant force.
1-1. Elastic force: springs control the retraction of a ballpoint pen tip; rubber bands can bind items.
1-2. Wind force: wind turns windmills and makes kites fly in the air.
1-3. Buoyant force: swim rings and kickboards help people float more easily on the water’s surface.
2. Whether an object sinks or floats in water is related to its shape. Objects that would normally sink can float more easily if changed into a container-like shape.
3. In addition to buoyancy, water can move objects and transmit power. For example, flowing water drives a water wheel, a water jet can wash away dirt, and a water gun can knock down an empty can.
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中文：
單元二活動一 力的現象有哪些
1.生活中常見各種力的現象，有些力可以使物體改變形狀；有些力可以使物體改變運動狀態。例如：雙手壓膠泥、雙手拉橡皮筋、用腳踢球。
2.力的大小、方向和作用點會影響力對物體的作用，稱為力的三要素。施力時，碰觸物體的位置稱為力的作用點。利用線段的長短表示力的大小，用箭頭可以表示施力的方向。
活動二 磁力有什麼特性
1.磁鐵具有磁力，可以吸引鐵製的物品。
1-1.能被磁鐵吸引：長尾夾、迴紋針、釘書針、剪刀(刀片部位)
1-2.不能被磁鐵吸引：色紙、彩色筆、橡皮擦、膠帶、鉛筆、十元硬幣。
2.長條形磁鐵不同部位，磁力強弱不同，通常 兩端的磁力比較強，稱為「磁極」，分別是 N極、S極。
3.磁力強弱與磁鐵大小不一定有關，可以用吸引迴紋針的數量來比較磁力強弱。磁力越強，可以吸引的迴紋針數量就越多。
4.當磁鐵的磁極（N極和S極）互相靠近時，相同磁極會互相推斥，不同磁極會互相吸引。
5.利用磁鐵可以吸引鐵製品，及隔著物品仍具有磁力的特性，可以快速又方便的分離地上的沙土和鐵粉。
6.生活中常利用磁鐵來吸引鐵製品，或利用磁鐵異極相吸的特性來固定物品。
7.磁鐵兩旁附加鐵片可以增加磁鐵的吸力。如鉛筆盒、門擋等物品上，可以發現磁鐵旁附加兩片鐵片。
活動三 還有什麼不一樣的力
1.生活中還有不同種類力的應用，例如彈力、風力、浮力等。
1-1.彈力：彈簧能控制原子筆的筆心縮回、橡皮筋能綁住物品等。
1-2.風力：風讓風車轉動、讓風箏在空中飄揚。
1-3.浮力：游泳圈和浮板讓人更容易浮在水面上等。
2.物體在水中的沉浮和物體的形狀有關，原本會沉在水中的物體改變成容器形狀後，比較容易浮在水面上。
3.水除了具有浮力，也可以使物體移動、傳送動力。例如流水推動水車轉動、水柱可以沖走髒汙、水槍能將空罐射倒等。
