Mechanics Flashcards
Define scalar and vector quantities
scalar quantities have magnitude only, vector quantities also have a direction
How is a vector resolved?
split it into two components at right angles to each other
What do arrows on a free-body diagram represent?
direction and size of the forces acting on an object
What is an object in equilibrium
What is an object in equilibrium?
object at rest or moving with constant velocity
Define the moment of a force about a point
moment = force x perp distance from the point to the line of action of the force
What is the principle of moments?
for equilibrium, sum of clockwise moments about a point = sum of anticlockwise moments about the point
What does a displacement time graph show?
how distance travelled by an object from a fixed point and direction change with time
How is a steady speed represented on a displacement-time graph?
straight line with constant gradient
How can instantaneous velocity at a particular time be found on a curved v-t graph?
by drawing a tangent to the curve at the given time
What does a curved line on a v-t graph represent?
changing acceleration
What does a value of zero on an object’s a-t graph indicate?
object moving with constant velocity at given time
What are the conditions for an object to be in free fall?
It only has its weight acting on it
Give the properties for the acceleration of a projectile
acceleration is due to gravity, it is always downwards, and only affects the vertical motion of the object
If an object is only moving vertically, what direction is regarded as positive?
upwards
What is the acceleration for an object launched horizontally with an initial velocity U?
accelerates downwards at 9.81m/s/s
What happens to the trajectory of a projectile if air resistance acts on it?
downward trajectory will be steeper than upward trajectory
Define inertia
tendency of an object to remain in a steady state at rest, or moving in a straight line at a constant speed
State Newton’s first law of motion
velocity of an object will only change if a force is acting on it
State Newton’s second law of motion
acceleration of an object is proportional to the resultant force on the object, and inversely proportional to the mass of the object
why do forces occur in pairs?
Newtons third law - whenever two objects interact with each other, they exert equal and opposite forces on each other
What are the properties of a pair of forces related by Newton’s third law?
same size; act on separate objects; act in opposite directions; along the same line; same type
What is the principle of conservation of momentum?
total momentum before collision = total momentum after collision
What is conserved in elastic collision?
kinetic energy
What is the relationship between force and momentum?
f = change in mv / t
State Newtons second law in terms of momentum
Force acting on an object is equal to rate of change in momentum
state the relationship between momentum and impulse
impulse = change in momentum (mv - mu)
What does the area under the line of a f-t graph represent?
impulse of the force
Define power
rate of energy transfer or rate of work done
State the relationship between power, work done and time
p = change in w/t
Define efficiency
measure of how much energy is wasted in a n energy transfer
State the principle of conservation of energy
Energy cannot be created or destroyed, only transferred
give the equation used to calculate the change in an object’s gravitational potential energy store
E = mgh
Give the equation used to calculate the amount of energy in an object’s kinetic store
E = (1/2)mv^2
Give the equation used to calculate the amount of energy in an object’s elastic potential store
E = (1/2)kl^2
