Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

PHYSICS · Stage 7 · Chapter 2: Forces

Physics 2.7 Chapter 2 Review: Forces

5 min read 5 parts Lesson 7 of 7

0%read
Lesson summary

2.7 Chapter 2 Review: Forces — Alhussan International Academy — Physics (Stages 7–9) notes: Revise mass, weight, gravitational field strength, resistance in fluids, streamlining and changing motion.Mass — the amount of matter in an object, measured in kilograms, and it does not c…

  • Values of g
  • Observation
  • Weaker gravity
  • No atmosphere
  • Streamlined shape
  • Diving bird

Section 1 of 5Mass, weight and gravitational field strength

  • Mass
    • the amount of matter in an object, measured in kilograms, and it does not change with place.
  • Weight
    • the force of gravity on the object, measured in newtons (N), and it depends on the strength of gravity where the object is.
  • Formula
    • weight = mass × gravitational field strength, W = m × g.
  • Values of g
    • about 10 N/kg on Earth, 1.6 N/kg on the Moon and 3.7 N/kg on Mars.
      • (about one sixth of Earth's)
  • Astronaut
    • one with a mass of 65 kg has a weight of 650 N on Earth, and on Mars the mass is still 65 kg but the weight is only about 240 N.

Section 2 of 5Golf on the Moon

  • Observation
    • when Alan Shepard, the fifth person to walk on the Moon, hit a golf ball it travelled much further than on Earth.
  • Weaker gravity
    • the ball is pulled down more slowly, so it stays in the air longer.
  • No atmosphere
    • there is no air resistance to slow the ball down.

Section 3 of 5Resistance in fluids and streamlining

  • Drag
    • a solid moving through a liquid or gas experiences a resistive force, called water resistance or air resistance, that acts against its motion.
  • Streamlined shape
    • it has a narrow, smooth, pointed front so the fluid flows round it easily and drag is small.
  • Diving bird
    • it folds its wings close to its body before hitting the water.
    • This protects the wings from injury.
    • It makes the bird more streamlined, which reduces water resistance and lets it enter the water faster and more cleanly.
  • Not a forward force
    • streamlining increases speed by reducing drag, not by adding a forward force.

Section 4 of 5Fair test of streamlining

  • Method
    • make three different shapes from modelling clay and time how long each takes to sink to the bottom of a tank of water.
  • Independent variable
    • the shape.
  • Dependent variable
    • the time to fall.
  • Control variables
    • the mass of clay, the depth and temperature of the water and the release height.
  • Repeats
    • repeat each shape and find a mean.
  • Prediction
    • the most streamlined shape has the least drag, so it should sink fastest.

Section 5 of 5Forces and changes in motion

  • Balanced forces
    • they leave an object stationary or moving at constant speed in a straight line.
  • Unbalanced forces
    • they change the speed or direction of motion.
  • Shape
    • forces can also change the shape of an object.
  • Circular motion
    • a force acting at right angles to the motion makes the object move in a circle, and in orbits the force is gravity.

Last updated: