Year 7 Science · Unit 3 · Lesson 1
Apply Worksheet
Learning Goals
Match each force to an example
Write the letter of the matching example next to each force. Each letter is used once.
| Force | Letter | Example |
|---|---|---|
| Friction | A. A tow rope pulling a broken-down car | |
| Tension | B. A compass needle swinging round to point north | |
| Normal force | C. A rubbed balloon sticking to a wall | |
| Magnetism | D. A bike’s brake pads rubbing on the wheel rim | |
| Electrostatic force | E. A diving board pushing up on a diver standing on it |
1. A force arrow shows two pieces of information about a force. Name them, and say how the arrow shows each one.
What does the force do?
For each situation, write C (contact) or NC (non-contact), name the force, and say which change it causes: start moving, stop, change direction or change shape.
| Situation | C or NC? | Name of the force | Change it causes |
|---|---|---|---|
| 1. A goalkeeper’s gloves stop a fast shot | |||
| 2. A magnet under a table makes a rolling steel ball curve toward it | |||
| 3. A child squeezes a stress ball flat | |||
| 4. An apple comes loose and begins to fall from a branch |
2. A kayaker paddles forward. Her paddling pushes the kayak forward with a force of 75 N, and water drag pushes back on the kayak with a force of 50 N. Using the scale 1 cm = 25 N, draw the kayak as a box and draw both forces as labelled arrows to scale. Then say which force is bigger, and how your drawing shows it.
Read the data: forces on a skydiver
Scenario
A skydiver jumps from a plane. Table 1 shows the two forces on the skydiver at two moments during the fall. The skydiver and the parachute are treated as one object.
| Force | Direction | Moment 1: falling, parachute closed (N) | Moment 2: a while after the parachute opens (N) |
|---|---|---|---|
| Gravity | Down | 750 | 750 |
| Air resistance | Up | 400 | 750 |
Source: made-up values for this worksheet.
3. Sort the two forces in Table 1 into the two families of forces from the lesson. Give a reason for each, based on what air is made of and where Earth is.
4. (a) At which moment would the two arrows on a force diagram be the same length? (b) At the other moment, describe how the two arrows would compare. (c) Suggest why the gravity arrow does not change when the parachute opens.
5. A surfer rides a wave at Bondi Beach. None of the forces on the surfer and her board can be seen. Name three forces acting on the surfer and board. For each, say whether it is a contact or non-contact force and give its direction. Then explain why scientists draw forces like these as arrows.
Match each force to an example
Friction → D; Tension → A; Normal force → E; Magnetism → B; Electrostatic force → C.
Question 1
Magnitude (size): shown by the arrow’s length, longer means bigger (1). Direction: shown by the way the arrow points (1). [2 marks]
What does the force do?
1 mark per row, all three cells correct. 1: C; push from the gloves (applied force; accept normal force); stop. 2: NC; magnetism; change direction. 3: C; push or squeeze from the hands (applied force); change shape. 4: NC; gravity; start moving. [4 marks]
Question 2
Forward arrow 3 cm long, labelled push from paddling, 75 N (1). Backward arrow 2 cm long, labelled water drag, 50 N (1). The forward push is bigger: its arrow is longer (1). [3 marks]
Read the data: forces on a skydiver
3. Air resistance is a contact force: air is matter, and its particles hit the skydiver and parachute (1). Gravity is a non-contact force: Earth is far below and pulls with nothing touching in between (1). [2 marks]
4. (a) Moment 2, both 750 N (1). (b) At moment 1 the gravity arrow (750 N) is almost twice as long as the air resistance arrow (400 N) (1). (c) Gravity is Earth pulling on the skydiver, and opening the parachute does not change the skydiver or Earth; the parachute only changes how hard the air pushes (1). [3 marks]
Question 5
Marking guide: 1 each for three correct forces with type (gravity, NC; water pushing up, or buoyancy, C; water drag, C; accept air resistance, C); 1 all three directions correct (gravity down, buoyancy up, drag backward); 1 an arrow shows both the size (length) and direction of a force; 1 arrows can be compared at a glance to see which force is bigger, which a photograph cannot show. [6 marks]
Model answer: Gravity pulls the surfer and board down; it is non-contact. The water pushes up on the board (buoyancy), and water drag pulls backward against it; both are contact forces because the water touches the board. A force cannot be photographed, but an arrow shows its size by its length and its direction by where it points, so two forces can be compared at a glance.
Common error: calling the whole scene “contact” or “non-contact”. Classify one force at a time.