Materials Flashcards
(22 cards)
What do you think we mean by the term “elastic limit”?
The elastic limit is the point beyond which the material you are stretching becomes permanently stretched so that the material does not return to its original length when the force is removed.
Point P is called the “limit of proportionality”
Maximum force that can be applied before extension stops being proportional to force
Point E is called the “elastic limit”
Maximum force that can be applied before an object becomes permanently distorted (deformed) – it won’t return to its original shape.
After the elastic limit, compare the load to the extension.
You get a large increase in extension for a small increase in load
What do you think a restoring force is?
The restoring force is the force a spring exerts to restore the spring to its original length (equilibrium position)
Parallel springs
k1 and k2 each have their own spring constants
If a constant force is exerted on the spring, the springs will be extended (compressed) by the same amount.
This system of two parallel springs is equivalent to a single spring, of spring constantk.
k = k1 + k2
SPRINGS IN SERIES
The force applied on two springs in series is the same on each of the springs.
How to find energy transferred on a Hookes law graph
The energy transferred to the potential energy store of the spring for where it obeys Hooke’s Law can be calculated by the area under the graph
What does the hysteresis loop tell us?
The energy per unit volume transferred to internal energy of the elastic material
What is stress
Stress is the internal resistance, or counterforce, of a material to the distorting effects of an external force or load per unit of cross-sectional area.
The atoms slowly pull apart from one another
Eventually the forces between atoms will become so great, they separate completely – the wire will break
The tensile force is experienced by the whole wire at point A INTERNALLY
What is strain
Strain is the response to the internal stresses on a wire
When a material is loaded with a force, it produces a stress, which then causes a material to deform
Strain is the measure of the extension of a material in the direction of the applied force
What is density
Density is how much matter (mass) there is in a given space (volume). The less the separation between particles, the greater the density.
How does density change as a substance (i.e. water) changes state from solid to liquid to gas
Energy is transferred to the potential energy store as a substance changes state.
Particles will move further apart due to weaker forces between them.
This will increase the volume.
Since mass is conserved, density will decrease.
Where will the force on the fluid be the greatest and where will it be the least? Why
As pressure increase with depth, the force experienced by the cube will always be greater at the bottom than the force acting at the top.
What is upthrust
Upthrust is the weight of the water that has been displaced by a submerged object
What is Archimedes principle
The weight of the fluid displaced is called the upthrust. It is equal to the weight.
Define laminar flow
In laminar flow, all the fluid elements flow in the same direction, and none of the streamlines cross over. It usually occurs at lower velocities and with streamlined objects. The word ‘laminar’ means flow in layers, and it is as if there are layers of fluid sliding over each other. In laminar flow, the ‘layers’ towards the middle tend to flow faster because friction decreases.
Define turbulent flow
Turbulent flow occurs at higher velocities or with non streamlined objects, when the flow lines become chaotic and mixed up. Eddies - small whirlpools - form where the flow gets mixed up.
What is viscosity
viscosity η is the measure of how resistant a fluid is to flow
It is a measure of how resistance there is between two adjacent layers in laminar flow
How are viscosity, temperature, velocity and work related?
Increasing temperature decreases viscosity which decreases the work needed to get the fluid to flow and thus the fluid will flow with an increased velocity.
What is viscous drag
Viscous drag is the resistive force experienced by an object moving in a fluid
