Measuring Forces: Direction and Size

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🔵 Part 1: Understanding Forces

A force is a push or pull that can change an object's speed, direction, or shape. Forces have both a size (measured in Newtons, N) and a direction.

1. What unit is used to measure the size of a force?

Kilograms (kg)

Newtons (N)

Metres (m)

Joules (J)

2. Which of the following are examples of a push force? (Select ALL that apply)

Kicking a football

Pulling open a door

Pressing a button on a keyboard

Picking up a bag

Pushing a shopping trolley

3. A force arrow (vector) tells us two things about a force. What are they?

① The _________________ of the force ② The _________________ of the force

4. If a force arrow is drawn longer, what does that tell us?

The force is slower

The force is larger / stronger

The force is going upward

The force has no direction

✏️ Part 2: Drawing and Describing Forces

Draw force arrows on the diagrams below. Use a longer arrow for a bigger force and label each arrow with the force name and an estimated size in Newtons.

5. A book is sitting still on a desk. Two forces act on it: gravity pulling it down and the normal force pushing it up. Draw and label both force arrows on the box below. (Hint: if the book is not moving, the arrows should be equal in size!)

6. A student kicks a soccer ball to the right with a strong force of about 40 N. Draw a force arrow on the ball below to show this force. Make sure your arrow shows the correct direction and is a good length for 40 N.

7. Look at the two scenarios below. Circle the one with the greater force and explain how you know.

🅐 A gentle breeze pushing a leaf 🅑 A strong wind pushing a tree

8. Estimate the size of the force needed for each action below. Choose from the box: 1 N | 10 N | 100 N | 500 N

a) Lifting a glass of water: __________ N

b) Pushing a car out of a ditch: __________ N

c) Picking up a pencil: __________ N

d) Lifting a school bag: __________ N

🌟 Part 3: Thinking Deeper

9. Two students are having a tug-of-war. Student A pulls left with 60 N. Student B pulls right with 80 N. In which direction will the rope move? Explain why.

10. In your own words, explain why it is important to show BOTH the direction AND the size of a force when drawing a force diagram.

📋 Answer Guide (Teacher Reference)

Q1: Newtons (N)

Q2: Kicking a football ✓ | Pressing a button ✓ | Pushing a shopping trolley ✓

Q3: ① Direction ② Size (magnitude)

Q4: The force is larger / stronger

Q5: Two equal-length arrows — one pointing down (gravity/weight) and one pointing up (normal force)

Q6: One arrow pointing to the right, relatively long to represent 40 N

Q7: 🅑 Strong wind — the force is greater because it can move a much larger, heavier object

Q8: a) 10 N | b) 500 N | c) 1 N | d) 100 N (accept reasonable estimates with justification)

Q9: The rope moves to the right because Student B applies a greater force (80 N > 60 N). The net force is 20 N to the right.

Q10: Accept answers that mention: knowing only the size doesn't tell us where the force is going; knowing only the direction doesn't tell us how strong it is — you need both to fully describe and predict what will happen to an object.