NEWTONINE
THE IB PHYSICS LAB
Hooke’s law is a core practical. Exam questions often show a force–extension graph and ask you to:
- Determine the spring constant k from the gradient.
- Identify the limit of proportionality (point where graph stops being a straight line).
- Explain that beyond the elastic limit the spring is permanently deformed.
Key formula: F=kx (when using applied force) – the gradient of a force–extension graph gives k.
MYP command terms used:
- *Determine*: Find the value, often from a graph.
- *Explain*: “The spring obeys Hooke’s law until the extension reaches X cm because the graph is a straight line through the origin.”
Always convert extension to meters.
When calculating k from a graph, select two points far apart on the straight section.
Many past questions ask: ‘Why does the spring not return to its original length after a large force?’ – Answer: it has exceeded its elastic limit and undergone plastic deformation.
Newton’s First Law: An object remains at rest or in uniform motion unless acted on by a resultant force.
Free‑body diagrams are a frequent exam task. Arrows represent forces; their length indicates magnitude.
If an object is stationary or moving at constant speed, forces are balanced → resultant force = 0.
Calculation: Fnet=ma, where Fnet is the resultant force. If mass is in kg and acceleration in m/s², force is in newtons (N).
Draw free‑body diagrams with arrows touching the object, labelled clearly.
Never include ‘centrifugal force’ – it doesn’t exist in MYP.
If an object accelerates, the resultant force is in the direction of acceleration.
Q1. A spring with a constant of 50 N/m is stretched by 0.1 meters. What restoring force is exerted by the spring?
Q2. Which of the following is a non-contact force?
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