Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.4Unit 3: Forces, motion and pressure

Turning forces — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions

5 min read 9 parts Lesson 4 of 7 1 quiz

📚 Cambridge Checkpoint Physics 0893 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

2.4 Turning forces — CHECKPOINT PHYSICS 0893 notes: Describe turning forces and calculate moments, including balancing a seesaw.Examples — pushing a door handle, a bicycle pedal or pulling a door make an object turnLever = the object that turnsPivot = the point around which a lev…

  • Human body
  • Writing it
  • Finding force
  • Finding distance
  • Heavier person
  • Prediction

Part 1 of 7Turning effect of a force

Examples
  • Examples pushing a door handle, a bicycle pedal or pulling a door make an object turn
Lever
Lever the object that turns
Pivot
Pivot the point around which a lever turns
Human body
  • Human body a bent arm acts as a lever with the elbow as the pivot

Part 2 of 7Moment of a force

Moment
Moment the turning effect of a force
Force
  • Force the bigger the force, the bigger the moment
Distance
  • Distance the greater the distance from the pivot to where the force acts, the greater the moment
Equation
  • Equation moment = force × distance

Part 3 of 7Unit of moment

Unit
  • Unit newton metre, written Nm
Writing it
  • Writing it use an upper case N and a lower case m
Distance
  • Distance measured from the pivot to the line of action of the force, in metres

Part 4 of 7Calculating moments

Door
  • Door a pull of 35 N at 0.8 m from the hinge gives a moment of 28 Nm
Arm
  • Arm a 20 N weight at 0.25 m from the pivot gives a moment of 5 Nm
Finding force
  • Finding force force = moment ÷ distance
Finding distance
  • Finding distance distance = moment ÷ force

Part 5 of 7Balancing

Seesaw
  • Seesaw it is a type of lever with the pivot in the middle
Balanced
  • Balanced the moments on both sides of the pivot are equal and opposite
Example
  • 600 N at 2 m gives 1200 Nm, so an 800 N person must sit 1200 ÷ 800 = 1.5 m from the pivot
Heavier person
  • Heavier person sits closer to the pivot to balance a lighter person further away

Part 6 of 7Investigating moments

1
Pivot a metre rule on a clamp stand with an elastic band and newton meter attached by a loop of string.
2
Move the string loop as far from the pivot as possible and record the distance.
3
Pull the rule down a fixed distance and record the force.
4
Move the newton meter closer to the pivot and repeat, pulling down the same distance each time.
5
Record results in a table with distances in metres.
6
Plot a graph of force against distance and describe the pattern.

Part 7 of 7Result of the moment investigation

Prediction
  • Prediction the force needed increases as the distance from the pivot decreases
Pattern
  • Pattern a smaller distance needs a larger force for the same turning effect
Improvement
  • Improvement repeat measurements and read the newton meter at eye level to improve accuracy

Key terms

TermMeaning
MomentTurning effect of a force.
LeverObject that turns around a pivot.
PivotPoint around which a lever turns.
Newton metreUnit of moment, Nm.
BalancedHaving equal and opposite moments.

Avoid these mistakes

1
Writing the moment unit as nm — use Nm with a capital N.
2
Measuring distance from the wrong point — it is measured from the pivot.
3
Thinking only force matters — distance from the pivot matters too.
4
Thinking a seesaw balances when forces are equal — it balances when moments are equal.

Last updated:

\n