3.4 Materials Flashcards
What happens to a solid object when it is compressed or subjected to tension?
The spacing of the atoms in the solid is altered.
The forces between individual atoms are small, but because there are so many of them, a large force is necessary for an appreciable change in shape or size of the solid. usually when the force is removed the solid returns back to its original shape.
Define elasticity
Elasticity is the property of a body to resume its original shape or size once deforming force or stress has been removed.
Define deformation
Deformation is the change in shape or size of an object. If the material returns to its original shape then the deformation is elastic; if not, then the deformation is plastic.
What would you happen if an object which is elastic has a forced removed from it?
It will return back to its original shape.
What would you happen if an object which is plastic has a forced removed from it?
When the deforming force is removes, the object would not return back to its original shape or size. This is because it has exceeded its elastic limit.
What is an objects elastic limit?
An objects elastic limit is the force beyond which the atoms can no longer return to their original arrangement.
What is a tensile force? What would this look like on a spring and how wound it affect it?
Tensile forces cause tension in an object.
For there to be a tension in a fixed, stretched wire it must have equal and opposite forces on it at either end. This would cause the wire to increase in length and have a positive extension.
What is a compressive force? What would this look like on a spring and how wound it affect it?
Compressive forces cause compression in an object. The forces acting in this situation are also equal and opposite in direction, but they are acting towards each other and will result in a decrease in the length of the spring or a negative extension.
What does the graph of force against extension look like when stretching a wire?
What is Hooke’s law?
Hooke’s law states that the extension of an object is proportional to the force that causes it, provided that the elastic limit is not exceeded.
What is the equation for Hooke’s law?
F=kx
force= spring constant x extention
What is the spring constant?
The spring constant tells us how much force is required per unit of extension.
For example, a spring constant of 6mm-1 means it makes 6N to cause an extension of 1mm.
The spring constant only can be used when the material is undergoing elastic deformation- when the deformation is plastic, the force per unit extension is no longer constant.
What do we usually plot on the x-axis?
independent variably (change)
What do we usually plot on the y-axis?
Dependent variable (cause)
What do we plot of each axis on a graph where the gradient is the spring constant?
The graph of tension force against extension isn’t like most graphs as the independent variable is on the y-axis ad the dependent variable is on the x-axis. Therefore, extension (m) is plotted on the x-axis and force (N) is plotted on the y-axis
What would the line look like on a graph if the load is taken off a spring after the spring has gone past it’s elastic limit?
