4. Mechanics & Materials Flashcards
What is a vector?
A physical quantity that has a direction as well as a magnitude
Examples of vectors?
- field strength
- force
- momentum
- weight
- velocity
- acceleration
- displacement
What is a scalar?
A physical quantity that is not directional
Examples of scalars?
- density
- charge
- resistance
- work done
- energy
How can a vector be represented?
By an arrow
What does the length of an arrow representing a vector determine?
The magnitude of the vector quantity
How to resolve vectors into their horizontal and vertical components?
- use angle of vector (Θ)
- for sinΘ
- then for cosΘ
If two forces act on an object, when is equilibrium achieved?
When the two forces are equal and opposite
If three forces act on an object, when is equilibrium achieved?
When the resultant of any two of the forces is equal and opposite to the third force
What are the ways to work out forces on an object when it is in equilibrium?
- vector triangle
* resolve the components
What is the centre of gravity of an object?
The point through which the entire weight of the object may be considered to act
Word equation to calculate the moment of a force?
Force x Perpendicular distance from the line of action of the force to the pivot
What is the principle of moments?
For any object that is in equilibrium, the sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about that same point
What is a couple?
A pair of equal and opposite forces, not acting in the same straight line
What is the turning effect that couples create called?
A torque
How to calculate the torque of a couple?
torque = one of the forces x perpendicular distance between them
What are the two conditions for equilibrium?
- there is no net (resultant force)
2. there is no turning effect (moment) about any point
What is the centre of mass of a body?
The point on an object where the mass may thought to be concentrated
How to find COM of symmetrical objects?
Along the line of symmetry, or where multiple lines of symmetry intersect
How to find COM of non-symmetrical objects?
If an object swings freely, when it stops the COM is on a vertical line passing through the pivot
When an object is in equilibrium, what is true of the vertical forces?
They are equal in magnitude and opposite in direction
When an object is in equilibrium, what is true of the horizontal forces?
They are equal in magnitude and opposite in direction
When an object in equilibrium is supported at one point, what is the support force equal to?
It is equal and opposite to the total downward force acting on the object
How to calculate average speed?
distance / time