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Key Stage 3 (KS3) – Year 7 National Curriculum

Year 7 Physics: Forces as Vectors and Resultant Diagrams

Comprehensive video walkthrough, core summary notes, formulas, step-by-step worked examples, and interactive quiz.

Senior Examiner: Fiaraz Iqbal Subject: Physics Duration: 10:00 Updated: August 2026

Key Learning Objectives

By the end of this lesson and revision module, Year 7 students will be able to:

Topic Summary & Essential Notes

In Year 7 Physics, quantities are classified into two groups: Scalars (which have only size or magnitude, such as mass, time, speed, temperature) and Vectors (which have both a magnitude and a specific direction, such as force, velocity, acceleration, weight). Forces are represented by arrows: the length of the arrow shows the force's strength in Newtons (N), and the arrowhead points in the direction of action. When multiple forces act on an object, the combined overall force is called the Resultant Force. If resultant force = 0 N, forces are balanced (the object stays at rest or continues at constant speed). If resultant force > 0 N, forces are unbalanced and the object accelerates in the direction of the resultant force.

Key Rules, Formulas & Definitions

Resultant Force (Opposing Forces)
F_resultant = Forward Force − Backward Force (e.g. Thrust − Friction)
Newton's First Law (Balance)
If Resultant Force = 0 N → Object is stationary or moves at constant velocity.
Scalars vs Vectors Examples
Scalars: Distance, Speed, Mass, Energy, Time | Vectors: Displacement, Velocity, Force, Weight, Acceleration

2 Step-by-Step Worked Examples

Study these model solutions to understand how examiners award method and accuracy marks:

Worked Example 1

Worked Example 1: Finding Resultant Force and Motion

Question: A speed boat engine provides 500 N of thrust forward, while water drag and air resistance provide 350 N backward. Calculate the resultant force and describe the motion.

Step-by-Step Solution:

  1. Step 1: Calculate resultant force. F_resultant = 500 N (forward) − 350 N (backward) = 150 N forward.
  2. Step 2: Determine motion effect. Because the resultant force is greater than zero and acts forward, the forces are unbalanced.
  3. Step 3: State conclusion. The boat accelerates (speeds up) in the forward direction.
Final Answer: 150 N forward; boat accelerates forward.
Senior Examiner Insight: Always specify the direction (e.g. 'forward', 'to the right') when reporting a vector or resultant force.
Worked Example 2

Worked Example 2: Balanced Forces on a Skydiver

Question: A skydiver of weight 800 N reaches terminal velocity. State the size and direction of the air resistance force acting on them.

Step-by-Step Solution:

  1. Step 1: Definition of terminal velocity. Terminal velocity is a steady, constant speed where acceleration = 0.
  2. Step 2: Balance condition. Zero acceleration means resultant force = 0 N.
  3. Step 3: Calculate drag. Air resistance must exactly equal the downward weight: 800 N upwards.
Final Answer: 800 N acting upwards.
Senior Examiner Insight: Terminal velocity is a classic exam question: always state that upward air resistance equals downward weight, so resultant force is zero.

Common Pitfalls & Examiner Warnings

Avoid these common mistakes frequently identified by examiners in Key Stage 3 assessments:

Common Mistake: Confusing Mass (kg, scalar) with Weight (N, vector)
Mass is the amount of matter in kg; Weight is the gravitational force pulling that mass downwards in Newtons.
Common Mistake: Assuming a moving object MUST have an unbalanced force
An object moving at constant speed in a straight line has a resultant force of zero (balanced forces).
Common Mistake: Omitting the direction of a vector
Saying '10 N' without specifying 'to the right' or 'upward' is incomplete for vector descriptions.

Interactive Self-Check Quiz (3 Questions)

Test your understanding before checking the full worked answer and examiner mark scheme:

Question 1 of 3
Which of the following is a VECTOR quantity?
A) Mass
B) Speed
C) Velocity
D) Time
Click to Reveal Answer & Mark Scheme
Correct Answer: C) Velocity
Detailed Explanation: Velocity is speed in a given direction, making it a vector. Mass, speed, and time are all scalars.
Mark Scheme & Scoring Points: 1 mark for Velocity.
Question 2 of 3
A box is pulled to the right with 40 N and to the left with 40 N. What is the resultant force?
A) 80 N to the right
B) 0 N (Balanced)
C) 40 N upwards
D) 1 N
Click to Reveal Answer & Mark Scheme
Correct Answer: B) 0 N (Balanced)
Detailed Explanation: 40 N − 40 N = 0 N. The forces are balanced, so there is no change in motion.
Mark Scheme & Scoring Points: 1 mark for 0 N or Balanced forces.
Question 3 of 3
A tug-of-war team pulls left with 950 N while the other team pulls right with 800 N. What happens?
A) Resultant force is 150 N to the left; the rope accelerates left.
B) Resultant force is 1,750 N.
C) The rope stays completely stationary.
D) Resultant force is 150 N to the right.
Click to Reveal Answer & Mark Scheme
Correct Answer: A) Resultant force is 150 N to the left; the rope accelerates left.
Detailed Explanation: 950 N − 800 N = 150 N towards the left. The rope accelerates towards the side with greater force.
Mark Scheme & Scoring Points: 1 mark for 150 N to the left.
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