Year 11 / Linear motion and force
Draw forces on one object.
A free-body diagram includes external forces acting on one selected object: weight, normal force, tension, friction and applied forces as appropriate. Constant velocity requires zero net force, not zero individual forces.
Net force equals mass times acceleration. Newton’s third-law pair acts on different objects, so those two forces do not cancel on a single-object diagram. A normal force is perpendicular to the contact surface and need not always equal weight.
A net force changes motion
Explore the relationship
Applied force points right; a fixed 10 N force points left. Right is positive.
Acceleration / m s⁻²
Tap or focus a plotted point to read its values.
View plotted data as a table
| Series | Mass / kg | Acceleration / m s⁻² |
|---|---|---|
| Acceleration / m s⁻² | 1 | 15 |
| Acceleration / m s⁻² | 1.15 | 13.0435 |
| Acceleration / m s⁻² | 1.3 | 11.5385 |
| Acceleration / m s⁻² | 1.45 | 10.3448 |
| Acceleration / m s⁻² | 1.6 | 9.375 |
| Acceleration / m s⁻² | 1.75 | 8.57143 |
| Acceleration / m s⁻² | 1.9 | 7.89474 |
| Acceleration / m s⁻² | 2.05 | 7.31707 |
| Acceleration / m s⁻² | 2.2 | 6.81818 |
| Acceleration / m s⁻² | 2.35 | 6.38298 |
| Acceleration / m s⁻² | 2.5 | 6 |
| Acceleration / m s⁻² | 2.65 | 5.66038 |
| Acceleration / m s⁻² | 2.8 | 5.35714 |
| Acceleration / m s⁻² | 2.95 | 5.08475 |
| Acceleration / m s⁻² | 3.1 | 4.83871 |
| Acceleration / m s⁻² | 3.25 | 4.61538 |
| Acceleration / m s⁻² | 3.4 | 4.41176 |
| Acceleration / m s⁻² | 3.55 | 4.22535 |
| Acceleration / m s⁻² | 3.7 | 4.05405 |
| Acceleration / m s⁻² | 3.85 | 3.8961 |
| Acceleration / m s⁻² | 4 | 3.75 |
| Acceleration / m s⁻² | 4.15 | 3.61446 |
| Acceleration / m s⁻² | 4.3 | 3.48837 |
| Acceleration / m s⁻² | 4.45 | 3.37079 |
| Acceleration / m s⁻² | 4.6 | 3.26087 |
| Acceleration / m s⁻² | 4.75 | 3.15789 |
| Acceleration / m s⁻² | 4.9 | 3.06122 |
| Acceleration / m s⁻² | 5.05 | 2.9703 |
| Acceleration / m s⁻² | 5.2 | 2.88462 |
| Acceleration / m s⁻² | 5.35 | 2.80374 |
| Acceleration / m s⁻² | 5.5 | 2.72727 |
| Acceleration / m s⁻² | 5.65 | 2.65487 |
| Acceleration / m s⁻² | 5.8 | 2.58621 |
| Acceleration / m s⁻² | 5.95 | 2.52101 |
| Acceleration / m s⁻² | 6.1 | 2.45902 |
| Acceleration / m s⁻² | 6.25 | 2.4 |
| Acceleration / m s⁻² | 6.4 | 2.34375 |
| Acceleration / m s⁻² | 6.55 | 2.29008 |
| Acceleration / m s⁻² | 6.7 | 2.23881 |
| Acceleration / m s⁻² | 6.85 | 2.18978 |
| Acceleration / m s⁻² | 7 | 2.14286 |
| Acceleration / m s⁻² | 7.15 | 2.0979 |
| Acceleration / m s⁻² | 7.3 | 2.05479 |
| Acceleration / m s⁻² | 7.45 | 2.01342 |
| Acceleration / m s⁻² | 7.6 | 1.97368 |
| Acceleration / m s⁻² | 7.75 | 1.93548 |
| Acceleration / m s⁻² | 7.9 | 1.89873 |
| Acceleration / m s⁻² | 8.05 | 1.86335 |
| Acceleration / m s⁻² | 8.2 | 1.82927 |
| Acceleration / m s⁻² | 8.35 | 1.79641 |
| Acceleration / m s⁻² | 8.5 | 1.76471 |
| Acceleration / m s⁻² | 8.65 | 1.7341 |
| Acceleration / m s⁻² | 8.8 | 1.70455 |
| Acceleration / m s⁻² | 8.95 | 1.67598 |
| Acceleration / m s⁻² | 9.1 | 1.64835 |
| Acceleration / m s⁻² | 9.25 | 1.62162 |
| Acceleration / m s⁻² | 9.4 | 1.59574 |
| Acceleration / m s⁻² | 9.55 | 1.57068 |
| Acceleration / m s⁻² | 9.7 | 1.54639 |
| Acceleration / m s⁻² | 9.85 | 1.52284 |
| Acceleration / m s⁻² | 10 | 1.5 |
Explore: Vary the applied force across the opposing force and watch the acceleration reverse.
A 4 kg cart is pulled right with 18 N while friction is 6 N left.
- Net force = 18 − 6 = 12 N right.
- a = = 3 right.
Assumed knowledge
Vectors in one dimension.
Learning checkpoints & source
YOUR LEARNING CHECKPOINT- Apply Newton’s three laws.
- Use free-body diagrams and net force.
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