Mechanics and Materials Flashcards
What are the SUVAT equations?
- a= (v-u)/t
- s= 0.5(v+u)t
- s= ut +0.5at^2
- v^2 -u^2 =2as
What is Free fall?
when the only force is weight
What is the centre of mass?
the single point where the weight acts through
How do you find the centre of mass?
Hang an object from a point and draw a vertical line downwards from that point. Now hang the object from another point and draw another vertical line downwards.
- the centre of mass is were the lines cross
What is Moment?
the turning effect of a force
what does moment depend on?
the size of the force and how far away the force is applied from the turning point
What is the equation?
Moment= force x perpendicular distance from pivot
what is the principle of moment?
for a body to be in equilibrium, the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about the same point
What is a couple?
a pair of forces of equal size which act parallel to each other, but in opposite directions
What is Newton’s first law?
a body will remain at rest or at constant velocity unless acted in by a resultant forces
What is Newton’s second law?
the acceleration of a body is proportional to the force acted on it but inversely proportional to its mass
What is Newton’s third law?
If body A exerts a force on body B, then body B exerts a force on body A of the same magnitude, same type of force but opposite in direction
When is terminal velocity reached?
- constant driving force, no resultant force, i.e. no acceleration
What is work done?
the amount of energy transferred when a force acts on an object and moves it over a distance
What is Power?
the rate of work done
what are the equations for power in mechanics?
- P= WD/t
- P= Fv
What is the principle of conservation of energy?
Energy can not be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change.
What is Hooke’s law?
the extension of an elastic object, like a spring, is directly proportional to the force applied to it, as long as the force does not exceed the elastic limit
What is elastic deformation?
when the material returns to its original shape once the forces are removed
what is plastic deformation?
when the material is permanently stretched beyond elastic limit
What is brittle behaviour?
when an object breaks, suddenly cracks. little plastic behaviour
what is a fracture?
when the material completely breaks
what are tensile forces?
-forces that stretch the material
-stress is positive
what are compressive forces?
-forces that squash the material,
-stress is negative
what is the equation for stress?
-units?
stress= force/cross sectional area
-pascals
what is the equation for strain?
- units?
extension/ original length
- no units
what is breaking stress?
the stress required to break the material
what is the elastic strain energy?
the energy stored in the stretched material
what is the equation for elastic work done?
WD= 0.5Fx 𝑥
what is the equation for elastic potential energy?
E= 0.5k𝑥^2
what does Young’s modulus represent?
the stiffness of a material
what is the equation for Young’s modulus?
YN= stress / strain
What is the difference between static and dynamic equilibrium
-Static: no resultant force or resultant moment. i.e. stationary
- Dynamic: no resultant force but moving at constant velocity
What will the affect of air resistance have on the maximum speed and trajectory of a body?
- Speed: it will achieve a lower max speed and will reach a terminal velocity
- Trajectory: becomes flatter and shorter, smaller range and peak
