Materials Flashcards
What is a tensile force?
A force that produces extension, stretches
What is a compressive force?
A force that reduces the length of a material
What is Hooke’s law?
The applied force is directly proportional to the extension up until the limit of proportionality,
F=kx
What is k?
The spring constant, or the stiffness of the material, measured in newton metres
How can we find force against extension or the spring constant?
Get a ruler and set it up with a stand that has a string and secure stand with G clamp
- Suspend masses from the spring
- Vary mass and record extension
- Find extension by subtracting from original
- Find force acting for each mass using f=ma
- Plot a graph of force against extension
- If hooke’s law is correct, the results should create a straight line through the origin
How can we reduce errors from this practical?
Take readings at eye level to reduce parallax error
What is the area under the curve equal to?
Elastic potential energy or work done
What is the formula for elastic potential energy?
1/2fx, f=kc, sub in to get 1/2kx^2
What is the equation for stress?
Amount of force divided by cross sectional area with a unit of pascals or Nm^-2
What is the equation for strain?
Extension divided by the original length, x/L
What is the ultimate tensile strength?
The greatest amount of stress that a material can withstand before reaching a breaking point
What is young’s modulus?
Tensile strength/tensile strain
F/A divided by x/L
=FL/Ax
What is the apparatus used to determine young’s modulus?
A table where a wire is clamped running along the table with a pulley on the end and we can attach a mass at the end of the wire, put a ruler on the table along with the wire
How can we carry out the experiment to determine Young’s modulus?
Adding the weight each time will change the extension so add a marker to the new length to work out the extension
The force will be equal to mg, the area of the wire can be found using a micrometer to find the diameter and then the original length of the wire can be found from the ruler
Take several readings along the wire and then find the average for the area
Plot force against extension x, the gradient = young’s modulus times area divided by length, rearrange to get E
What can we use to find the extension if it is too small to measure?
A travelling microscope to reduce the percentage uncertainty in our measurements
