6.10 Elasticity, Spring Constant, & Hookes Law Flashcards
When you apply forces to an object it can be stretched, compressed or twisted. What is this?
Deformation
To deform an object, how many forces do you need?
At least two
What can you call an object if it returns to its original shape after the forces are removed?
You can say the object is elastic and it has been elastically deformed
What can you call an object if it doesn’t return to its original shape when you remove the forces?
The object has been plastic and has been plastically deformed
What can you explain both elastic and plastic deformation with?
The particle model of matter
What happens in elastic deformation?
Solids are held in fixed shapes due to the forces between their particles. During elastic deformation the separation between particles changes so the forces between them also change. However, once the applied force has been removed, the particles return to their original positions within the substance
What happens in plastic deformation?
In plastic deformation, the separation and forces between particles change. However, the applied forces are too large, so when they’re removed the particles don’t return to their original positions. The object is permanently deformed
What is meant by extension?
The increase in length of a spring when its stretched
How do we work out extension?
Measure how the spring’s length changes as we add downwards force
When a material is supported at the top, why would the natural length be shorter than the whole length of the material?
The material’s own mass would be exerting a force downwards in the form of weight
Why does the spring not fall down when we add any mass?
The solid support will also be exerting an equal but opposite force upwards and this is why the spring doesn’t fall down when we add any mass. It’s being perfectly balanced by the support
What happens to the extension when we add more mass?
It increases proportionally
What is the amount of extension for a given force made dependent on?
The object’s spring constant, which is noted by the letter k
What does the spring constant of an object tell us?
How many newtons it would take to stretch the object by 1m
If a material is supported at the top and a mass is attached to the bottom, it stretches. In some cases, e.g. a spring, this relationship is linear. What does this mean?
The extension (or compression) of the stretched material is directly proportional to the load or force applied
The relationship between the extension of a material and the force is called Hooke’s law. What is the equation for this?
force exerted by a spring (N) = extension (m) x spring constant (N/m)
What does it mean when a spring and mass are in equilibrium (i.e. the spring isn’t stretching any further)?
The force applied on the spring (the weight of the mass) is equal to the force exerted by the spring upwards on the mass
What is an example of an object that behaves non-linearly?
Rubber bands
If a material is supported at the top and a mass is attached to the bottom, it stretches. In some cases, e.g. rubber bands, this relationship is non-linear. What does this mean?
The force is not proportional to extension
What is important to remember about elasticity and Hooke’s law?
That being ‘elastic’ doesn’t mean an object obeys Hooke’s law. Rubber bands are elastic objects. They return to their original shape when released, but they DON’T obey Hooke’s law
In a force/extension graph, the larger the spring constant the __________ the gradient
steeper
On a force/extension graph, how do you know if the object’s extension obeys Hooke’s law?
The line will be straight and the force and extension will be directly proportional
On a force/extension graph, how do you know the object’s extension doesn’t obey Hooke’s law?
The line will be curved and the spring will stretch more for each unit increase in force
On a force/extension graph, what is the gradient of a straight line equal to?
The spring constant of the object
What is the point on a force/extension graph called where the line starts to curve?
Elastic limit or the limit of proportionality
On a force/extension graph, what happens after the elastic limit or limit of proportionality?
Hooke’s law no longer applies and the object wont necessarily go back to its original shape, meaning that it will have been permanently deformed
Applying forces to an object can cause it to: (3)
- Bend
- Compress
- Stretch
