Movement And Shape Flashcards
Elastic materials definition
Materials that return to their original shape
Examples of elastic materials
Rubber
Lycra
Plastic materials definition
Materials that do not return to their original shape when the force is removed
Examples of plastic materials
Polymers
Play doh
Plasticine
Brittle materials definition
Materials that will break rather than change shape
Examples of brittle materials
Ceramics
Glass
Wrought iron
What happens to the extension of a weight is added at the bottom of the spring?
Increases in length when it is stretched
As we increase the amount of mass on the spring what happens?
The extension increases proportionally
If the spring has not overstretched (for example one weight), what would the graph look like? The extension against the weight
It would be a straight line starting at the origin which has a constant gradient (which would mean the extension is directly proportional to the weight)
Hooke’s Law
If a stretched object produces a graph with a constant gradient, we say that it obeys Hooke’s Law.
It is a law that says that the extension of an elastic object is directly proportional to the force applied.
Do all springs behave the same?
No, some might extend more or less if the same force is applied.
For example, if Spring K extended more than Spring M, we would say that Spring M is the stiffest spring and spring K is the least stiff spring
Stretching springs to their limits
If more weights are added, the springs might get ‘overloaded’ and the graph might look different.
It might stop becoming proportional and the line stops being a straight line. This point is called the Limit of Proportionality.
If it does stop being elastic, it happens at a point called the Elastic Limit. You can’t tell by looking at the graph but all we know is that it is beyond the limit of proportionality.
Stretching Rubber
When stretched, rubber behaves differently to a metal spring. The line is a bit more irregular. It is stiff to begin with, then less stiff then gets stiffer again as more weight is added.
Elastic potential energy
When a spring is stretched, we say that we ‘do work’ on it which means that we transfer energy to it. This energy is stored as Elastic Potential Energy in the stretched object.
Load definition
The force applied
Measured in Newtons
Extension definition
How much longer compared to original length - measured in mm, cm or m
The centre of mass
An imaginary point where we can consider all of the mass of the object to be located. It is also the point where we can say that gravity acts on the object and is therefore also known as the Centre Of Gravity.
What is a turning moment?
A turning effect of a force
What does the turning moment depend on?
Size of the force
Perpendicular distance of the line of action from the pivot point of rotation
How to see a moment in any situation
Look for the pivot point of rotation
Look for the force that will make it rotate
Example of a spanner
The pivot point is where the screw is and the force is at the end of the spanner in which we hold to turn it. And therefore, the line of action is there at the end too.
The perpendicular distance is the distance from the line of action to the pivot
Moments equation
Moment = Force x perpendicular distance from the line of action of the force to the pivot
Force is measured in Newtons
Distance is measured in metres
Triangle - moment at the top, force in the left and distance in the right
Balancing moments
Moments make things turn so we describe the direction of turn as being anti-clockwise or clockwise.
When something is not rotating, the moments acting on the object would be balanced and we say that the object is therefore in equilibrium. And therefore, in order for it to be in equilibrium:
Sum of anti clockwise moments = sum of clockwise moments
This is known as the Principal of Moments
A seesaw is an example of this. If a person is sitting on the left and a person on the right. The person on the left is creating the anti-clockwise moment about the pivot and the right person is creating the clockwise moment about the pivot.
We can use this principal to work out stuff we don’t know. We just make it into an equation using anti clockwise = clockwise
