Forces And Elasticity (HOOKE’S LAW) Flashcards
When you apply force to an object, three things may happen. List them.
Either they’ll stretch, compress or bend
What’s the requirement for an object to deform?
There must be more than one force acting upon it
What will happen instead of changing the shape if only one force acts upon the object?
It’ll just move in the direction the force pushes or pulls it in, instead of changing the shape.
Explain what it would mean if an object were to be elastically deformed
If an object could return to its original form (shape and length) after the force is removed, then that object was elastically deformed.
Explain what an elastic object is. List an example.
An elastic object is an object that’s been elastically deformed. An example would be a spring.
What does it mean for an object to be inelastically deformed?
This is when an object cannot return to its original shape and form after the forces are taken away.
How is work done with elastic and inelastic objects?
Work is done when a force stretches/compresses an object and causes energy to be transferred to the objects elastic potential energy store. If the object is elastically deformed, then ALL the energy would transfer to its elastic potential energy store.
What is the relation between extension and force?
They’re in direct proportion.
What is the equation used to prove that force is in direct proportion to extension?
F = ke or kx
What does the F stand for in F = ke or kx? Give units.
F stands for force. Units: newtons
What does the k stand for in F = ke or kx? Give units.
k stands for spring constant. Units are N/m
What does the e or x stand for in F = ke or kx? Give units.
e/x stands for extension, units: metres
The spring constant can change depending on a certain thing. What is that thing? Explain with an example.
Spring constant will depend on the material you’re stretching. A stiffer material/object, would give a greater spring constant (more force, less extension)
What does e/x mean in F = ke or kx? (hint: I’m asking for what it means not what it stands for)
Extension is the difference between the objects natural length and the length after it deforms. It only applies to stretching and compressing.
How would F = ke or kx work for compression?
e/x would have to be the difference between natural length and compressed length.
In what scenario would F = ke or kx not apply?
If the force is great enough, it won’t apply anymore
True or False: there isn’t a maximum amount of force you can apply for the extension to keep increasing proportionately.
False
There is a graph showing force against ext. for an elastic object. Where can you find the limit of proportionality?
The point where the straight, diagonal line meets a curve
What happens if you go above the maximum for the applied force?
Above the maximum and the extension and force will no longer be directly proportional.
What is the limit of proportionality on a graph?
It’s a point what marks the maximum for applied force. Above that point, the graph curves and ext. and force are no longer proportional.
Normally, graphs for force against ext. will show force on the y axis and ext. on the x axis. What would happen if it were swapped?
The line would still go in a straight, diagonal line up until the limit of proportionality but instead of curving downwards it’d curve upwards as force will be greater than ext. past that point.
What is Hooke’s law?
Hooke’s law states that force and extension are directly proportional to each other unless force exceeds the limit of proportionality.
What happens if the limit of proportionality is exceeded?
The object (if elastic) will be deformed and will not go back to its original shape. In fact it is now inelastic.
What is the formula for Hooke’s law?
F = ke or F = kx
What is spring constant? Where do you find it on the graph
It’s the gradient of a the force vs extension graph. The stiffer a spring, the steeper the gradient. Spring constant is a measure of how stiff a spring is
What is spring constant? Where do you find it on the graph
It’s the gradient of a the force vs extension graph. The stiffer a spring, the steeper the gradient. Spring constant is a measure of how stiff a spring is
Define Hooke’s law
Extension is directly proportional to force exerted, provided the elastic limit/limit of proportionality isn’t reached
Explain how the limit of proportionality affects a spring stretching
A single spring should return to its original length after being stretched. Force = extension is in motion and this all happens because the spring is elastic. However, after a certain force is exerted on it, it’ll start to extend more than the force acting on it. This is where the elastic limit is reached. If limit of proportionality is reached, the spring is then deformed and it now possesses the inability to return to its original shape. The spring is now ineleastic
Which store is energy of a stretched spring stored in? What’s the unit?
Elastic potential energy (unit Joules)
List three ways that you can calculate energy stored in a stretched spring and list the conditions for all three ways
Way one: you have to have a graph. If you have one, the area underneath the line/graph is the energy. This is normally in a shape of a triangle if the line obeys Hooke’s law.
Way two: use formula Ep = 1/2F *e. You can only use this formula if extension is in METRES
Way three: use formula Ep = 1/2k *e squared. To use this, e HAS TO BE IN METRES. And everything to do with E in the equation. So k also has to be in N/m.
