Forces & Elasticity Flashcards

All 15 cards in this deck

How many forces are needed to stretch, bend or compress an elastic object?

Two or more. e.g. a spring is pulled down by a weight while the clamp holds the top up.

What is elastic distortion?

A change of shape in which the object returns to its original shape and length when the force is removed. e.g. a spring stretched by a small weight.

What is inelastic distortion?

A change of shape in which the object does not return to its original shape when the force is removed. e.g. stretched plasticine or an over-stretched spring.

What is the equation linking the force on a spring, the spring constant and the extension (with units)?

$F = k \times x$ — force in N, spring constant in N/m, extension in m.

What is the equation for the energy transferred in stretching a spring (with units)?

$E = \tfrac{1}{2} \times k \times x^2$ — energy in J, spring constant in N/m, extension in m.

True or false? An extension given in cm can be put straight into $E = \tfrac{1}{2} \times k \times x^2$.

False. The extension must be converted to metres first. e.g. 12 cm becomes 0.12 m.

What are the steps to investigate how the extension of a spring varies with the force applied?

e.g. adding 1 N weights up to 5 N

1. Hang the spring from a clamp stand and measure its original length with a metre rule.

2. Add weights one at a time, measuring the new length each time (1 N, 2 N, 3 N...).

3. Extension = new length − original length; plot force against extension.

How can parallax error be reduced when measuring the length of a stretched spring?

Use a pointer fixed to the spring and a set square against the ruler, reading at eye level.

How is the spring constant found from a graph of force (y-axis) against extension (x-axis)?

It is the gradient of the straight-line (linear) part of the graph.

What is a linear relationship between force and extension?

Force is directly proportional to extension, so the force–extension graph is a straight line through the origin.

True or false? A curved force–extension graph shows a non-linear relationship between force and extension.

True. In a non-linear relationship equal increases in force do not give equal increases in extension, so the graph is not a straight line.

What is meant by the extension of a spring?

The increase in length of the spring: extension = stretched (final) length − original length.

What is the limit of proportionality of a spring?

The point where the force–extension graph starts to curve. Beyond it, extension is no longer proportional to force and $F = k \times x$ no longer applies.

How can the work done in stretching a spring be found from its force–extension graph?

It is the area under the graph, up to the extension reached.

When a force stretches or squashes a spring, which energy store is energy transferred to?

The spring's elastic potential energy store — work is done on the spring as it changes shape.