Module 3 - Springs Flashcards
Describe the criteria for an object to be compressed or stretched
- Two forces
- Equal in magnitude
- Opposite in direction
Why does the magnitude of the two forces that cause deformation need to be equal in magnitude
If they are not equal in magnitude then there will be a resultant force which will cause the object to accelerate rather than deform
What are the two main forces linked to strings and what type of deformation do they cause
- Tensile Forces: Cause extension due to tension
- Compressive Forces: Cause compression
What is meant by deformation
The change in shape due to tensile or compressive forces
What is meant by extension
- The change in length due to deformation
State Hooke’s Law
For a material up to its limit of proportionality, the force applied is directly proportional to the extension of the material
When will an object not follow Hooke’s law
When the material has been extended passed its limit of proportionality
What is the equation linked to Hooke’s law
F (Force) = k (Force constant) x X(Extension)
What is meant by the Force Constant
- It is a measure of the stiffness of the spring (N/m)
What is the relationship with the difficulty to stretch a spring and the springs Force Constant
- The greater the force constant of a spring for the same extension, a greater force is needed
How do you calculate the force constant of a spring
- Draw and F/x graph
- Find the gradient of the graph within its elastic region
What is meant by Elastic Deformation
- When an object is extended within its elastic limit so changes shape but returns to its original length once the force is removed
What is meant by Plastic Deformation
- When an object is extended passed its elastic limit so changes shape but does not returns to its original length once the force is removed
What is meant by stiffness
The extent to which an object deforms under stress
When you pull a string why can you say that tension is doing work
- We lose energy and the spring is gaining energy
What is the equation for elastic potential energy in 3 different forms
- Ep = 0.5 Fx
- Ep = 0.5 kx²
- Ep = 0.5 F²/k
Why is there a 0.5 in the calculation of elastic potential energy
The force required to stretch a spring from its original length to a given extension is not constant.
∙ It increases as the extension increases.
∙Hence, we need to use the average force in our equation for work done.
In series what is the total force constant
1/kt = 1/k1 +1/k2
In parallel what isthe total force constant
kt = k1 + k2
What is the relationship between Force constant and extension given a constant force
inversely proportional
What direction does the force in a stretched spring act
Opposite to the direction of the stretch
How is the permenant extension shown on a Fx graph
The distance between the rest lengths on the loading and unloading curve
Describe the deformation graph for metals
- Up until the limit of proportionality there is a straight line
- After the limit of proportionality, the graph gradient decreases
- Returning from unloading the graph is parallel to the elastice regionW
Describe the deformation graph for rubber
As the force increase the extension increases at a slow rate, until a point where as the force increases the extension increases at a fast rate, until its breaking point. (vice versa for unloading)
Desribe the key features of the deformation graph for rubber
- Doesnt obey hookes law
- Has no plastic deformation
- Loading and unloading graph forms a hysterisis loop
Describe the significance of each of the areas under the hysterisis loop
- Under the loading curve: area = work done to strech the spring
- Unde the unloading curve: area = elastic energy recovered as the material returns to its original shape
- Between the Hysterisis loop: area = internal energy lost while stretching
Describe the deformation graph of polythene
- Loading is the same as rubber
- Unloading is the same as metalD
Describe the features of the polythene’s deformation
- Doesn’t obey hookes law
- Low elastic limit, therefore a little force is required for plastic deformation
