Science 6th grade | UNIT 4: Forces and motion 4.2 How forces act booklet
Science 6th grade | UNIT 4: Forces and motion 4.2 How forces act booklet
- Unit 1: The human body
- Unit 2: Materials: properties and changes
- Unit 3: Rocks, the rock cycle and soil
- Unit 4: Food chains and food webs
- Unit 5: Forces and electricity
- Unit 6: Light and the solar system
When we drop a book it falls to the ground. Gravity pulls all objects downwards. But can forces act in other directions?
Activity 4.2 (Investigating direction of forces)
You will need: a book - a table - an elastic band - a magnet - an iron nail
Put the book on the table. Does it move?
What would happen to the book if the table wasn't there? Why?
Hook one end of the elastic band around your forefinger. Pull on the other end of the elastic band. In which direction does the elastic band move? Why?
Name the force acting on the elastic band. Hold the magnet above the nail. In which direction does the nail move? Why?
Name the force acting on the nail.
Forces can act in different directions. When you put the book on the table, the book will exert a downward force on the table. This force is caused by gravity pulling the book downwards. The force is the weight of the book. The reason the book doesn't fall is because the table exerts an upwards force on the book.
Force diagrams
We can show the direction of forces on an object in a drawing called a force diagram. Each force is shown as a force arrow. When the forces are equal, the force arrows are the same length.
Forces always act in pairs. In the picture, the book exerts a downward force on the table and the table exerts an upward force on the book. The two forces act in opposite directions.
Questions
1) a: Copy the drawing and add arrows to show the direction in which each of the forces act.
b: Is one force bigger than the other? Say why or why not.
2) When you stand still, why don't you sink into the ground? Draw a force diagram to explain your answer.
What you have learnt
- Forces act in different directions.
- Forces act in pairs. Each force in a force pair acts in the opposite direction to the other.
- Force diagrams show the direction and size of forces.
