CritABCD
A.2 · 7 · A.2 Forces and momentum · big picture (enrichment)

Force: the link between space and time

Imbalance drives motion. Force connects the three dimensions of space with time, and carries the present into the future.

SL+HLMedium14 minFree
Hook

Space has three dimensions and time has one. Is there a single quantity that ties both to the way things change?

Utkarsh laws of motion
1 / 4

Imbalance is the cause of motion

Rule 1
Imbalance is the cause of motion
Rule 2
The greater the imbalance, the more the motion
ONE IDEA, FOUR KINDS OF MOTION
Example of motionWhat movesThe imbalanceThe law
1 Transportationbulk movement of matterforces: 10 N one way, 2 N the other, so Fnet = 8 NNewton’s second law: Fnet = ma (acceleration)
2 Diffusionparticlesconcentration A ≠ B, with A > Brate of diffusion ∝ Δconcentration
3 Heat energyenergytemperature TA ≠ TB, with TA > TBrate of heat flow ∝ ΔT
4 Currentmovement of chargepotential VA > VBI ∝ ΔV, so V = IR (Ohm’s law)
no imbalance, no motion
Check 1 of 4

Which pair are BOTH equal to force?

Check 2 of 4

A constant 6.0 N force acts along a body’s path for 2.0 m. The energy transferred is…

Check 3 of 4

The same 6.0 N force acts for 2.0 s. The change in momentum is…

Check 4 of 4

In the imbalance table, what plays the role of the imbalance for an electric current?

Apply

Explain how force connects space and time, using two equations.

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Remember earlier lessons
From lesson A.2 · 2

F_net = …

From lesson A.2 · 5

Which quantity is a scalar?

Summary card

Key points

  • • Imbalance is the cause of motion; a bigger imbalance means more motion.
  • • Force = work done per unit displacement (space) = change in momentum per unit time (time).
  • • Given the present state and the force, the future (and the past) follows.

Formulas

  • WD / x = F = Δp / t

Key terms

Imbalance
:
a difference (of force, concentration, temperature or potential) that drives a flow
Work done
:
the way energy in one form (E₁) is converted into energy in another form (E₂); a force acting through a displacement

Common errors

  • • Mixing up energy per distance (force) with energy per time (power).
  • • Forgetting the condition: constant force along the displacement.
  • • Treating work done as a store of energy: it is the process that converts E₁ into E₂.
Checks solved: 0 of 4