Young’s Modulus

Define the following

• Strain

• Stress

• Brittle

• Elastic

Define the following

• Stress – The force applied per cross-sectional area of a material

• Strain – The extension in length resulting from stress

• Brittle – A material that breaks without plastic deformation

• Elastic – A material that returns to its original shape after deformation

Define the followingKey Word Definition Example

StiffDoes not easily change shape when force is applied

Glass

ElasticReturns to original shape when force is removed.

Copper

Plastic Remains deformed when force is removed Blu-tac

Ductile Can be readily pulled out into a thinner shape. Copper

Malleable Can be deformed under compression Copper

Strong Requires a large force to break it Steel

Brittle Easily cracks Glass

Tough Needs a large force to deform it Kevlar

Smooth Low friction surface PTFE

DurableProperties do not deteriorate with repeated loading and unloading

Bone

Stress vs Strain

• If you add a big enough stress on a wire, it will produce strain.

• Stress is the force applied per unit cross-sectional area.

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Things we will need to measure to start

• The diameter of the wire, at three points for accuracy

• The length of wire, the longer this is the better

• Work out the cross sectional area of the wire • Record the mass and convert into weight • Measure the extension (in metres)

The TableMass (kg) Weight (N) Area (m2) Stress

(N/m2)Length (m) Extension

(m)Strain

Working out uncertainty

• When you need to work out the uncertainty from two readings multiplied together or divided, we follow the following method.

• Work out the uncertainties as percentages.• For 5±0.5cm

Working out uncertainty 2

• Whether you are multiplying or dividing units, you will always add the uncertainties together.

• I measure the side of a cube to be 10±0.5cm

• What is its volume if all dimensions are the same?

• What is the uncertainty with that volume?