Science in Punggol study guide · Article 0015 of 20
A force is a push or a pull. Forces can change an object’s movement or shape: they can start motion, change speed, change direction or deform an object.
To explain a force, identify the object, the interaction and the change observed.
On this page: Find the push or pull · Describe what changes · Match the force to the situation · Worked question: pressing a sponge
Find the push or pull
Your hand pushes a door when you open it. A stretched spring can pull on an attached object. Some forces act through contact, while others act without direct contact.
Earth’s gravitational force pulls objects towards Earth. A magnet can attract a suitable magnetic material nearby. Neither requires the object to touch Earth or the magnet first.
A force is not the same thing as movement. A book resting on a table still experiences a downward gravitational force. The table provides an upward supporting force. These forces balance, so the book remains at rest.
Describe what changes
When a goalkeeper stops a ball, the ball’s speed changes. When a ball strikes a wall and rebounds, its direction changes. When a hand squeezes a sponge, the sponge changes shape.
More than one effect can occur together. Describe the effects supported by the question rather than assuming that any movement means the object became faster.
Compare before and after: was the object at rest, moving or already changing shape? What happened after the interaction? This makes an answer more precise than simply writing “a force acted.”
Forces also have directions. A labelled arrow can show a push to the right or gravitational force towards Earth. State which object experiences the force so that the explanation stays clear.
Match the force to the situation
Gravity explains why a dropped object falls. Friction helps explain why a block sliding across a surface slows. An elastic spring exerts a force when stretched or compressed. Magnetic force explains attraction to a suitable magnetic material.
On a Punggol walk, a carried bag, a pushed door and a braking bicycle offer different examples. Each explanation should identify the particular object and interaction being considered.
A soft ball on a clear, level surface can illustrate force effects. A gentle push starts it moving; another gentle push from the side can change its direction. This shows an effect but does not measure the size of the applied force.
Forces are interactions, not a supply stored in a moving object. A sliding block does not stop because it has “used up its force.” Friction from the surface acts against its sliding motion and slows it.
Worked question: pressing a sponge
Question: A pupil presses a sponge with her hand. The sponge becomes flatter. Explain the effect of the force.
Worked explanation: The hand exerts a pushing force on the sponge. The force changes the sponge’s shape, making it flatter.
Common mistake: “The force makes the sponge move.” That does not describe the change asked about. The question supplies evidence of a shape change, so the answer should address that effect.
Use the same approach in a movement question: name the source of the force, the object it acts on and the specific change. Then check that each part matches the evidence.
