weirdfacts
Year 11 / Linear motion and force

Trade height for motion.

Work is energy transferred by a force acting through a displacement. For a constant force parallel to displacement, W = Fs. Net work changes kinetic energy. Near Earth, raising a mass changes gravitational potential energy by mgΔh.

When resistive effects are negligible, mechanical energy is conserved. With friction, some mechanical energy becomes internal energy. In an elastic collision, both total momentum and total kinetic energy are conserved; in an inelastic one, only the momentum rule remains if external impulse is negligible.

INTERACTIVE MODEL

Height becomes speed

READ THE GRAPH

Explore the relationship

Released from rest; no drag or friction.

Final speed / m s⁻¹03.6757.3511.0314.702.557.510Vertical drop / m
Final speed / m s⁻¹

Tap or focus a plotted point to read its values.

View plotted data as a table
Explore the relationship
SeriesVertical drop / mFinal speed / m s⁻¹
Final speed / m s⁻¹00
Final speed / m s⁻¹0.1666671.80739
Final speed / m s⁻¹0.3333332.55604
Final speed / m s⁻¹0.53.1305
Final speed / m s⁻¹0.6666673.61478
Final speed / m s⁻¹0.8333334.04145
Final speed / m s⁻¹14.42719
Final speed / m s⁻¹1.166674.78191
Final speed / m s⁻¹1.333335.11208
Final speed / m s⁻¹1.55.42218
Final speed / m s⁻¹1.666675.71548
Final speed / m s⁻¹1.833335.99444
Final speed / m s⁻¹26.26099
Final speed / m s⁻¹2.166676.51665
Final speed / m s⁻¹2.333336.76264
Final speed / m s⁻¹2.57
Final speed / m s⁻¹2.666677.22957
Final speed / m s⁻¹2.833337.45207
Final speed / m s⁻¹37.66812
Final speed / m s⁻¹3.166677.87824
Final speed / m s⁻¹3.333338.0829
Final speed / m s⁻¹3.58.28251
Final speed / m s⁻¹3.666678.47742
Final speed / m s⁻¹3.833338.66795
Final speed / m s⁻¹48.85438
Final speed / m s⁻¹4.166679.03696
Final speed / m s⁻¹4.333339.21593
Final speed / m s⁻¹4.59.39149
Final speed / m s⁻¹4.666679.56382
Final speed / m s⁻¹4.833339.73311
Final speed / m s⁻¹59.89949
Final speed / m s⁻¹5.1666710.0631
Final speed / m s⁻¹5.3333310.2242
Final speed / m s⁻¹5.510.3827
Final speed / m s⁻¹5.6666710.5388
Final speed / m s⁻¹5.8333310.6927
Final speed / m s⁻¹610.8444
Final speed / m s⁻¹6.1666710.9939
Final speed / m s⁻¹6.3333311.1415
Final speed / m s⁻¹6.511.2872
Final speed / m s⁻¹6.6666711.431
Final speed / m s⁻¹6.8333311.573
Final speed / m s⁻¹711.7132
Final speed / m s⁻¹7.1666711.8519
Final speed / m s⁻¹7.3333311.9889
Final speed / m s⁻¹7.512.1244
Final speed / m s⁻¹7.6666712.2583
Final speed / m s⁻¹7.8333312.3909
Final speed / m s⁻¹812.522
Final speed / m s⁻¹8.1666712.6517
Final speed / m s⁻¹8.3333312.7802
Final speed / m s⁻¹8.512.9074
Final speed / m s⁻¹8.6666713.0333
Final speed / m s⁻¹8.8333313.158
Final speed / m s⁻¹913.2816
Final speed / m s⁻¹9.1666713.404
Final speed / m s⁻¹9.3333313.5253
Final speed / m s⁻¹9.513.6455
Final speed / m s⁻¹9.6666713.7647
Final speed / m s⁻¹9.8333313.8828
Final speed / m s⁻¹1014
Final speed / m s⁻¹: 0

Explore: Increase the starting height and compare final speed with energy.

Ek=12mv2ΔEp=mgΔhW=ΔEE_k=\tfrac12mv^2\qquad\Delta E_p=mg\Delta h\qquad W=\Delta E
WORKED EXAMPLE

A 2 kg object speeds up from 3 to 5 ms1\mathrm{m}\,\mathrm{s}^{-1}.

  1. Net work = 0.5 × 2 × (525^{2}323^{2}).
  2. Net work = 16 J.
Assumed knowledge

Squaring velocities.

Learning checkpoints & sourceYOUR LEARNING CHECKPOINT
  • Use work–energy relationships.
  • Distinguish elastic and inelastic collisions.
QCAA Physics · Unit 2 · Linear motion and force
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