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Unit 3: Forces, motion and pressure

GRADE 7 – Unit 3: Forces, motion and pressure — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 9 parts Lesson 1 of 8 1 quiz

📚 HIA International - Grade 7 Hub / Topical Revision
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Lesson summary

GRADE 7 - Unit 3: Forces, motion and pressure — HIA INTERNATIONAL notes: Explain forces, speed, moments, pressure and diffusion.Force — a push or pull measured in newtons.Balanced forces — equal and opposite, causing no change in movement.Unbalanced forces — cause speeding up, sl…

  • Force diagram
  • Falling objects
  • Average speed
  • Sketch graph
  • Graph with values
  • Balanced seesaw

Section 1 of 9Balanced and unbalanced forces

Force
  • Force a push or pull measured in newtons.
Balanced forces
  • Balanced forces equal and opposite, causing no change in movement.
Unbalanced forces
  • Unbalanced forces cause speeding up, slowing down or a change of direction.
Force diagram
  • Force diagram arrow length shows the size of each force.
Falling objects
  • Falling objects a parachute increases air resistance until the forces balance and the speed becomes constant.

Section 2 of 9Speed

Speed
Speed distance ÷ time, measured in m/s.
Distance
Distance speed × time; time = distance ÷ speed.
Average speed
  • Average speed total distance divided by total time.
Units
  • Units keep them consistent and show them in the answer.

Section 3 of 9Distance-time graphs

LineMeaning
HorizontalStationary
Straight upward slopeConstant speed away from the start
Steeper lineFaster
Straight downward slopeConstant speed back to the start
Sketch graph
  • Sketch graph has no numbers on the axes.
Graph with values
  • Graph with values speed = distance ÷ time read from the axes.

Section 4 of 9Moments

Lever
Lever an object that turns about a pivot.
Moment
Moment the turning effect of a force.
Equation
  • Equation moment = force × distance from the pivot, in Nm.
Balanced seesaw
  • Balanced seesaw moments on both sides of the pivot are equal and opposite.

Section 5 of 9Pressure in solids

Pressure
Pressure force ÷ area, in N/m2 (or N/cm2, N/mm2).
Small area
  • Small area increases pressure, as in a knife, pin or nail.
Large area
  • Large area decreases pressure, as in a camel foot or snow shoe.

Section 6 of 9Pressure in liquids and gases

Pressure in liquids and gases
Liquid pressure
  • Liquid pressure increases with depth because of the weight of liquid above, and acts equally in all directions.
Gas pressure
  • Gas pressure caused by particles colliding with the container walls.
More gas particles or higher temperature
  • More gas particles or higher temperature more force, so higher pressure.
Atmospheric pressure
  • Atmospheric pressure highest at sea level and falls with altitude.
Pressure cooker
  • Pressure cooker raises the pressure and temperature of steam.

Section 7 of 9Diffusion

Diffusion
Diffusion the overall random movement of particles from higher to lower concentration.
Gases and liquids
  • Gases and liquids particles move randomly, so smells and dyes spread.
Equal concentration
  • Equal concentration diffusion stops, but particles keep moving.
Faster diffusion
  • Faster diffusion bigger concentration difference and higher temperature.

Section 8 of 9Key terms

TermMeaning
ForceA push or pull measured in newtons.
SpeedDistance travelled per unit of time.
MomentForce multiplied by distance from the pivot.
PressureForce divided by area.
DiffusionMovement of particles from high to low concentration.
PivotThe point a lever turns about.
Atmospheric pressureThe pressure of the air at a point in the atmosphere.
ConcentrationThe number of particles in a volume.

Section 9 of 9Exam technique

1
Writing speed = distance × time.
2
Saying a horizontal line on a distance-time graph means slow movement — it means stationary.
3
Giving moment in N or N/m — it is in Nm.
4
Saying gas pressure comes from particles pushing each other — it comes from collisions with the walls.
5
Saying diffusion stops particle movement — particles still move randomly.

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