Topic 2 - Mechanics Flashcards
What is displacement?
The distance in a given direction from a fixed reference point
What is velocity?
The rate of change of displacement with time (speed with a direction)
What is speed?
The rate of change of distance with time
What is acceleration?
The rate of change of velocity with time
What is the difference between instantaneous and average values?
An instantaneous value gives a value at an exact instant.
An average value gives an average value for a fixed amount of time.
What is the final velocity of an object when its acceleration is uniform?
v = u + at
What is the acceleration of a body falling in a vacuum near the Earth’s surface?
g = 9.81 ms–2
What is the effect of air resistance on falling objects?
- Air is forced to move out of the path of the object
- As air resistance increases, the rate of increase in velocity becomes less
- Eventually the object reaches a constant, maximum speed known as the terminal velocity
A: no air resistance
B: yes air resistance
What does an object’s terminal velocity depend on?
- Cross-sectional area
- Shape
- Weight
How can the velocity be found in displacement–time graph?
By calculating the gradient of the line
How can the instantaneous velocity be found from an exponential displacement–time graph?
By calculating the gradient of the tangent to the line at that instant
How can the acceleration be found in a velocity–time graph?
By calculating the gradient of the line
What is the area under a velocity–time graph equal to?
The change of displacement
What is the area under an acceleration–time graph equal to?
The change of velocity
Summarise the graphs of motion
What is relative velocity?
The difference between two velocities measured in the same frame of reference
What is the simplest form of a force?
A push or a pull
What are accelerations caused by?
Forces (push)
What can forces do to the shape of an object?
Alter it and cause deformation
What are different types of forces
- Weight
- Tension and compression
- Reaction forces
- Friction and air resistance
- Upthrust
- Non-contact forces
What is the expression for weight?
W = mg
What is the rule of reaction forces?
If two objects are in contact with each other, then each must exert an equal force on the other
What is air resistance?
A force that opposes motion
What is friction?
Opposing force when objects are in contact
What is upthrust?
A force exerted vertically upwards on any object which is in a fluid
What are non-contact forces?
- Gravitational force
- Magnetic force
- Electric force
- Nuclear forces
What are the components of forces for the following diagram?
FA = mgsinθ
FB = mgcosθ
What is Newton’s first law of motion?
An object will remain at rest, or continue to move in a straight line at a constant speed, unless a resultant force acts on it
What is translational equilibrium?
An object that has no resultant force acting on it is saidto be in translational equilibrium (resultant force is zero)
What are examples of Newton’s first law?
- Objects at rest with no sideways forces
- Horizontal motion at constant velocity
- Vertical motion of falling objects
- Horizontal acceleration
How can equilibrium be achieved for a mass that is not in equilibrium?
If two forces are acting on an object, a third external force can be added that is equal in magnitude to the resultant force of the other two
What is Newton’s second law of motion?
Acceleration is proportional to the force:
F = ma
Force equals the rate of change of momentum:
What is linear momentum?
Mass multiplied by velocity
p = mv
What is impulse?
The product of force and the time for which the force acts
impulse = F∆t = m∆v
What is the area under a force–time graph equal to?
The impulse (change of momentum)
What is said about the conservation of momentum?
All momentum is conserved.
Always true with no exceptions
What is Newton’s third law of motion?
To every action there is an equal and opposite reaction
What are examples of Newton’s third law?
- If you pull a rope, the rope pulls you
- If the Earth pulls a person, the person pulls the Earth
- If a fist hits a cheek, the cheek hits the fist
- If the Sun attracts the Earth, the Earth attracts the Sun
- If a boat pushes down on the water, the water pushes up on the boat
What is work?
The energy transfer that occurs when an object is displaced by using a force
What is the work done if the force is constant and in the same direction as movement?
W = Fs
What is the work done if the force is not in the same direction as the displacement?
W = Fscosθ
What is the area under a force–displacement graph?
Work done
What are different forms of energy?
- Gravitational (potential) energy
- Nuclear (potential) energy
- Chemical (potential) energy
- Electric (potential) energy
- Elastic strain (potential) energy
- Thermal energy (heat)
- Radiant energy
- Kinetic energy
- Internal energy
- Mechanical wave energy (sound and water waves)
What is potential energy?
Stored energy. Potential energies exist where there are forces between objects
What is kinetic energy?
Energy that involves moving objects
What are types of energies that transfer energy?
- Electrical energy
- Thermal energy
- Radiant energy
- Mechanical waves
What is the principle of conservation of energy?
Energy cannot be created or destroyed, it can only be transferred from one form to another.
(the total amount of energy in the universe is constant)
What is the change in graviational potential energy?
∆EP = mg∆h
What is the formula for kinetic energy?
EK = 1/2mv2
What is the equation for kinetic energy with momentum?
Useful when dealing with the motion of atomic particles
What are the equations for doing work to change motion?
What is an elastic collision?
A collision in which the total kinetic energy of the masses is the same before and after.
What is an inelastic collision?
A collision in which some or all kinetic energy is transferred to other forms of energy
What is power?
The rate of transferring energy
What is the power transferred when travelling at constant velocity?
P = Fv
What is efficiency?
Draw a vector diagram to illustrate that the acceleration of a particle moving with constant speed in a circle is directed towards the centre of the circle
- The velocities are always directed along tangents to the circle
- A centripetal force is always acting perpendicularly to the velocity, inwards towards the centre
- Resultant force acting on the mass has the same magnitude but continuously changing direction
What is the expression for centripetal acceleration?
What is the force needed to make a mass move in a circle at constant speed?
