Mechanics Flashcards
What is a scalar with 2 examples
A magnitude of something, for example mass, energy
What is a vector with 3 examples
A quantity with both magnitude and direction, for example, displacement, acceleration, velocity
What is a moment
A turning effect of a force
Moment =
force x perpendicular distance from the pivot to the line of action of the force
What was does the principle of moments state
For a body to be in equilibrium, sum of clockwise moment about a point must equal sum of anticlockwise moment about that same point
What is a couple
A pair of forces of equal magnitude, acting parallel to each other in opposite directions
What is the mass of a body and what is it measured in
The amount of matter within a body; in kgs
What is weight defined as
The force experienced by a mass due to a gravitational field strength
Is weight a scalar or vector
A vector
What is displacement
How far an abject has travelled from starting point in given direction
Define velocity
Rate of change of an object’s displacement
Acceleration =
Change is velocity / change in time
What will acceleration look like on a D-T graph
A curve - upward sloping for acceleration, downward deceleration
How to find velocity from a D-T graph
Work out the gradient, which is the velocity
What does the gradient of a V-T graph show
Acceleration (as it =Δv/t)
How to find displacement on a V-T graph
Area under the graph
What is an object’s acceleration if it is free falling
Acceleration of g
What is Newton’s first law of motion
A body will have constant velocity (and direction) unless an external resultant force acts upon it
What does Newton’s second law state
Acceleration is proportional to force
Force =
Mass x acceleration
What does Newton’s third law state?
If object A exerts a forced on object B, then object B exerts an equal but opposite force back on A
What are the two types of friction
Dry (between solids) and fluid (drag, fluid or air resistance)
What does the effect of fluid friction depend on
Viscosity of the fluid and shape of the object
What is lift
An upward force acting on an object in a fluid
How does a car reach terminal speed
As car accelerates, the frictional forces acting against it increase. This reduces the resultant force on the car and reduces in acceleration. Eventually the car reaches a speed at which the frictional force is equal to the driving force; the car carries on at a constant speed
Momentum =
Mass x velocity
What is an elastic and inelastic collision
An elastic collision is where KE in conserved, whereas some is transferred to other forms in inelastic collisions
What is always conserved when 2 objects collide, assuming no external forces act
The momentum of the 2 objects
Define impulse
Force x time; the change in momentum
Define work
The amount of energy transformed from one form to another when a force causes movement
Give an example showing energy changes
Lifting up a box; gravity is the force opposed and GPE is the final energy form
Work done =
Force x distance moved
What is the area under a force/displacement graph
The work done
Define power
The rate of work done; the amount of energy transferred from one form to another per second
Power = (2)
change in work done / change in time
Force x velocity
What does the conservation of energy state
Energy cannot be created or destroyed; total energy in = total energy out
Efficiency =
useful output power / input power
Work done against air resistance =
Loss in GPE - gain in KE
For a falling object, what is loss in GPE equal to
Gain in its KE
