As the PSLE draws closer, students must be getting anxious with trying to memorize all the different science topics. Hence, we have created these detailed notes which contain popular questions and explanations on the topic, Forces.
Use this note to help strengthen your concepts about Forces for PSLE science and learn the answer structure to answer Forces open-ended questions.
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What is a Force?
A force is a push or a pull, when we push or pull an object, we are applying a force on it.
4 Types of Forces (P6 Syllabus)
1. Frictional Force
Explanation: Frictional force between surface of Object A and the surface of Object B
Effects of Frictional Forces:
- Slows down moving objects
- Stops moving objects
- Opposes movement
Practice Question #1: Bryan set up an experiment as shown below. He used a spring balance to pull two identical wooden blocks across ramp A and ramp B. Both ramps are made of different materials.
Correct Answer: The surface of A is rougher than B, hence there is more frictional force between the surface and the box opposing the pull force exerted on the box.
Practice Question #2: Bryan repeated his experiment using ramp A as shown below. He measured the force needed to pull the wooden block using a different angle x. The graph shows his results.
Correct Answer: As angle X of the ramp increases, the pulling force exerted on the box also increases.
2. Magnetic Force
Explanation: A magnet is an object made of iron or steel. It can attract (pull) or repel (push) magnetic objects.
Characteristics:
- Attract magnetic objects
- Has 2 poles where attraction is the strongest (North and South Poles)
- Unlike poles attracts each other and like poles repel each other
- Comes to rest in the North-South Direction when freely suspended
2 Ways to Make A Magnet
- Stroking a magnetic object with a magnet permanent magnet
- Using electricity to magnetize a magnetic object through electromagnetization.
Practice Question #1: The diagram shows Object B balanced by magnets A and X.
a) In the diagram, fill in N and S to show the poles of magnet X
b) Explain how Object B is balanced by magnet A
Correct Answer: a) N on top, S below. b) The magnetic attraction force between magnets A and X is the same as the gravitational force acting on object B.
Practice Question #2: Object B is replaced by Object C with a mass of 60g. Magnet X is also replaced by magnet Y. To balance Object C, fill in ‘N’ and ‘S’ to show the poles of magnet Y.
Correct Answer: S on top, N below.
3. Gravitational Force
Explanation: Gravitational force depends on height and mass. This is NOT to be confused with gravitational potential energy which depends on weight and mass.
Practice Question: Mr Aziz found that it requires more effort to climb up the stairs compared to going down. Give a reason for your answer.
Correct Answer: More effort is required when going up because he is going against the direction of gravity.
4. Elastic Spring Force
Explanation: A force exerted by a spring when it is stretched or compressed.
What can an elastic object do?
- Change shape when force is applied
- Return to its original shape when applied force is removed
Practice Question #1: The diagram below shows a bow and arrow and when the string of the bow was pulled back. Label the force acting on the arrow.
Correct Answer: Gravitational force acting on the arrow.
Practice Question #2: When the string was released, the arrow travelled in the path as shown below before hitting the ground at point B.
a) In terms of forces, explain the movement of the arrow from the point it was released at A till it hit the ground at B.
b)The activity was repeated with an arrow of a greater mass. Explain how this will affect the movement of the arrow.
Correct Answer:
a) The push force exerted on the arrow pushes it forward but it is weaker than the gravitational force exerted on the arrow hence the arrow was pulled down to the ground eventually.
b) The arrow will hit the ground faster. The increased mass of the arrow will result in more gravitational force acting on the arrow and pulling it down to the ground more.
