Mechanics Flashcards
Define scalar quantities
Has magnitude only.
Define vector quantities
Has magnitude and direction.
What are some examples of scalar quantities?
temperature mass distance energy speed density time
What are some examples of vector quantities?
velocity displacement acceleration force weight momentum
How can you calculate the resultant vector?
pythagoras
How can you calculate the final vector?
trigonometry
What is instantaneous velocity?
Velocity at a given point
Define speed
How fast something is moving (regardless of direction).
Define displacement
How far an object has travelled from its starting point in a given direction.
Define velocity
The rate of change of an object’s displacement.
Define acceleration
The rate of change of an object’s velocity.
What is meant by uniform?
Constant - e.g. uniform acceleration
Define weight
The force on an object due to gravity.
What is meant by free fall?
When the only force acting on the object is its weight, so it accelerates towards the ground.
What shape does a displacement-time graph have?
Accelerating object: always be a curve.
Uniform acceleration: gradient is constant
Constant velocity: straight
How do you find instantaneous velocity on a displacement-time graph?
Draw a tangent to the curve to a certain point and find its gradient.
What does a v-t graph represent?
Acceleration
- straight line = uniform acceleration
- steeper gradient = greater acceleration
What does the area under a v-t graph show?
Displacement of an object.
What does a a-t graph show?
How an object’s acceleration changes over time.
What are the features of a a-t graph?
height = object’s acceleration at that time
area under graph = object’s change in velocity
if a is 0 = constant velocity
What is Newton’s first law?
An object at rest stays at rest and an object in motion stay in motion unless acted upon by unbalanced forces.
What is Newton’s second law?
Acceleration is directly proportional to the magnitude of the net force and inversely proportional to the mass of the object. F = ma
What is Newton’s third law?
For every action, there is an equal and opposite reaction.
State the properties of pairs of forces in an interaction between bodies
- act in opposite directions
- equal magnitude
- same type of force
- act on same bodies
What is the principle of conservation of linear momentum?
Momentum is always conserved (when no external forces act).
Define the ‘moment of a force’
The turning effect of a force
What is the principle of conservation of energy?
Energy cannot be created or destroyed, only transferred to one store or another.
What are the two main types of friction?
Friction between:
- solids
- fluids (drag/air resistance)
What is terminal velocity?
When the friction force equals the driving force.
How does weight and air resistance act on a skydiver?
- leaves plane: accelerates (freefall)
- air resistance = weight (terminal velocity)
- after parachute: air resistance increases (bigger than their weight)
- slows down until new terminal velocity reached again
