Materials Flashcards
(35 cards)
What is Archimedes’ principle
- Upthrust magnitude=weight of fluid displaced by the body
What is upthrust
- When a body is fully or partially submerged in a fluid, pressure differences at different depths cause it to experience an upward force- upthrust
What is laminar flow
- Flow in layers
Characteristics of laminar flow
- Occurs at lower speeds and around streamlined objects
- Layers do not mix and are roughly parallel to each other
What happens in turbulent flow
- Flow is chaotic and subject to sudden change in speed and direction
- Large scale mixing of fluid layers
What are streamlines
- Lines of laminar flow
- At any point in each of these streamlines the velocity with time of the flow will be constant
What is viscous drag on objects
- The frictional force between layers of fluid being present when a solid moves through a liquid
When is viscous drag largest
- In turbulent flow rather than laminar flow
What does stokes law equation give us
- Formula for viscous drag for small spheres at low speeds in laminar flow
What is Hooke’s law
The force needed to extend a spring is proportional to the extension of the spring
When is Hooke’s law obeyed
- If material has not passed its limit of proportionality
What is Hooke’s law equation
Force=stiffness x extension
What is distortion
- A change in shape of an object
What is elastic distortion
- Temporary distortion- will go back to its original shape
What is inelastic/plastic distortion
- permanent distortion- will not go back to original shape
What is the elastic limit
- The maximum force a body can endure and still regain original shape and size
What is the limit of proportionality
The point where Hooke’s law ceases to be obeyed
What is elasticity
- The property a material has whereby it regains its original size and shape when a deforming force is removed
What is stiffness
- A measure of a body’s resistance to changes in size/shape
What is a yield point
- When a large extension is produced for a very small increase in force
- The material of the body is said to show ‘plastic’ behaviour
When do stress and strain occur
When forces deform an object it is said to be STRESSED. As a result the material becomes STRAINED
What is stress
- The force per unit area acting on a material
What is strain
The extension per unit original length
What is young modulus
The measure of the ability of a material to withstand changes in length with an added load