Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

Unit 3: Forces, motion and pressure

Forces and motion — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 2 of 8 3 quizzes

📚 HIA International - Grade 7 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

3.1 Forces and motion — HIA INTERNATIONAL notes: Explain balanced and unbalanced forces and their effects on the motion of objects.Force — a push or pull, measured in newtons (N).Force diagram — arrows show the size and direction of each force, and a longer arrow means a bigger f…

  • Forces on stationary objects
  • Contact force
  • Sideways forces
  • Drawing balanced forces
  • Starting to move
  • Up and down

Section 1 of 9Forces and force diagrams

Forces and force diagrams
Force
  • Force a push or pull, measured in newtons (N).
Force diagram
  • Force diagram arrows show the size and direction of each force, and a longer arrow means a bigger force.
Forces on stationary objects
  • Forces on stationary objects forces act on an object even when it is not moving.
Weight
  • Weight the pull of gravity towards the centre of the Earth.
Contact force
  • Contact force the push of the ground up on an object resting on it.

Section 2 of 9Balanced forces

Balanced forces
Balanced forces forces that are equal in size and opposite in direction.
Effect
  • Effect balanced forces cause no change in movement.
Stationary object
  • Stationary object a rock stays still because the weight and contact force balance.
Sideways forces
  • Sideways forces wind pushing on the rock is balanced by friction with the ground.
Drawing balanced forces
  • Drawing balanced forces use arrows of the same length pointing in opposite directions.

Section 3 of 9Unbalanced forces

Unbalanced forces
Unbalanced forces forces that are not equal in size and/or not opposite in direction.
Effect
  • Effect they cause a change in movement: speeding up, slowing down or changing direction.
Starting to move
  • Starting to move a push larger than friction makes the rock move in the direction of the larger force.
Up and down
  • Up and down the vertical forces stay balanced, so the rock does not move up or down.

Section 4 of 9Effects of unbalanced forces

Size of forcesDirectionResultEffect on motion
EqualOppositeBalancedNo change
EqualNot oppositeUnbalancedChange of direction
Not equalOppositeUnbalancedSpeeds up or slows down
Not equalNot oppositeUnbalancedChange of speed and direction

Section 5 of 9Slowing down with a parachute

Parachute opens
  • Parachute opens air resistance becomes larger than the weight, so the forces are unbalanced and the object slows down.
Slowing
  • Slowing as the object slows, air resistance decreases.
Constant speed
  • Constant speed the forces become balanced again and the object falls at a constant speed.

Section 6 of 9Changing direction

Tennis ball
  • Tennis ball the hitting force from the racket must be larger than the force from the ball to send it back.
Orbits
  • Orbits gravity on a planet is a constant unbalanced force that keeps it moving in a circle round the Sun.
Circular motion
  • Circular motion an object moving in a circle changes direction all the time, so a constant unbalanced force is needed.

Section 7 of 9Investigating balanced and unbalanced forces

1
Two people each hold a newton meter attached to a string with coloured tape on it.
2
Pull with equal forces so the tapes stay lined up.
3
Increase both forces equally and observe that the string does not move.
4
Make one force smaller and observe the string move towards the larger force.
5
Increase the difference between the forces and observe the effect.
Result
  • Result the larger the difference between the forces, the greater the effect on movement.
Analogy
  • Analogy the investigation models a tug of war, with the newton meters representing the two teams.

Section 8 of 9Key terms

TermMeaning
ForceA push or pull measured in newtons.
Balanced forcesForces equal in size and opposite in direction.
Unbalanced forcesForces not equal and opposite.
WeightThe force of gravity pulling an object towards the Earth.
Contact forceThe push of a surface on an object resting on it.
Air resistanceThe force of air opposing the motion of an object.
FrictionA force that opposes movement between surfaces.
Force diagramA diagram using arrows to show forces.

Section 9 of 9Exam technique

1
Saying no forces act on a stationary object — balanced forces act.
2
Saying balanced forces mean the object is still — it may move at constant speed.
3
Saying an object always moves in the direction of the larger force without a change — only unbalanced forces change motion.
4
Drawing balanced force arrows with different lengths.

Last updated: