02 - Mechanics Flashcards
What must always be true when using the SUVAT equations of motion?
The acceleration must be uniform - if the acceleration is changing, the equations are not valid.
What does the gradient of a distance-time graph represent?
Speed
What does the gradient of a displacement-time graph represent?
Velocity
What does the gradient of a velocity-time graph represent?
Acceleration
Describe the shape of a velocity-time graph for an object travelling with uniform acceleration.
If acceleration is constant, the gradient of the velocity-time graph will be constant and so it will form a straight line graph.
Describe the shape of a velocity-time graph for an object travelling with non-uniform acceleration.
If acceleration is not constant, the gradient of the velocity-time graph will change and so it will form a curve.
Compare the velocity-time graphs for a uniformly accelerating and a uniformly decelerating object.
• For an accelerating object, the gradient will be positive
• For a decelerating object, the gradient will be negative
What is a scalar quantity
A scalar quantity is one that has a magnitude but not a fixed direction.
What is a vector quantity?
A vector quantity is one that has a magnitude and a fixed direction.
Give five examples of scalar quantities.
- Distance
- Speed
- Mass
- Energy
- Temperature
Give five examples of vector quantities.
- Displacement
- Velocity
- Acceleration
- Momentum
- Force
How is a vector quantity represented on a diagram?
• As an arrow
• The direction of the arrow represents the direction of the quantity
• The length of the arrow represents the magnitude of the quantity
What does resolving a vector involve?
Splitting the vector into two perpendicular components (vertical and horizontal
How should the components of a proiectile be handled when carrying out calculations?
• The horizontal and vertical components are independent of each other and so should be treated separately
• SUVAT should be used separately for each component
If a projectile is moving freely under gravity, what can be said about the vertical acceleration?
The vertical acceleration will be the acceleration due to gravity and so will have a magnitude of 9.81 ms.
On a displacement/time graph what does a curve in the graph represent
Acceleration/deceleration
What does the area under the graph of a velocity/ time graph represent
Displacement
Which suvat equation would you use if u had : v , t , u and a
V = u + at
Which suvat equation would you use if u had : a , t , u and s
S = ut + 1/2at^2
Which suvat equation would you use if u had : u, v, a and s
v^2 = u^2 + 2as
Which suvat equation would you use if u had : s, u, v, t
S = 1/2(u + v) t
What does u stand for in the suvat equations
Initial velocity
What does the v stand for in the suvat equations
Final velocity
What are the 4 suvat equations
v = u+at
S = ut + 1/2at^2
v^2 = u^2 + 2as
S = 1/2 (u+v)t
State Newton’s first law
An object will continue to move with uniform velocity, unless it is acted on by resultant external force
What is newton’s second law?
F = ma
Only uses when the object experiences a resultant force (is accelerating or decelerating)
Can an object travelling with constant speed change direction, without an external force acting?
For an object to change direction, its velocity must change. This means there must be an acceleration. An acceleration cannot occur without an external resultant force acting.
Describe the forces acting on an object travelling at terminal velocity.
• The forces are balanced in both the vertical and horizontal components of its motion
• There is no resultant force, and therefore no acceleration
What is meant by terminal velocity?
For a given set of conditions, the terminal velocity is the maximum speed of the object. An object has zero acceleration at terminal velocity.
State the equation used to calculate the weight of an object.
W = mg
Weight = Mass x Gravitational Field
Strength
State Newton’s third law
Every action has an equal and opposite reaction
Describe in Newton’s third law pair of someone holding a mass
There is a normal contact force of it on you, and you are exerting a normal contact force on it
What are the conditions for Newton’s third law?
Equal in magnitude
Acting in opposite directions
The same type of force
Acting on different objects
When talking about Newton’s third law, what would you describe weight as
Weight is a gravitational force
What is the Newton’s third law pair of someone standing on Earth?
The gravitational force of the person on the Earth, and the gravitational force of the Earth on the person
State the equation for momentum.
p = mv
Momentum = Mass x Velocity
What is the unit of momentum?
kgms^-1
What is the consequence of the linear conservation of momentum?
The total momentum of a system before an event is always equal to the total momentum of the system after the event.
What is the law of the conservation of energy?
Energy cannot be created or destroyed, only transferred from one energy store to another
State the equation used to calculate the work done by a force.
W = F x s
Work Done = Force × Change in
Distance
What force is used when calculating the work done by a force over a distance?
The component of the force that is in the direction of the object’s motion.
What is the unit of work?
Joules, J
What is the work done by the force, F when it moves the object a distance of x? When F is at an angle
You work out the horizontal component so:
Work Done = Fcos(angle)x
What form of energy do all moving objects have?
All moving objects have kinetic energy.
State the equation used to calculate the kinetic energy of an object.
Kinetic Energy = ½ × Mass × Velocity^2
E = ½ mv^2
What form of energy does a raised object have?
Gravitational Potential Energy
State the equation used to calculate gravitational potential energy.
GPE = Mass × Gravitational Field
Strength x Height
E = mgh
What is power?
The rate at which energy or work is
done.
State 3 equations used to calculate power.
P= E/ t
P = Work done / time
P = force x velocity
What is the unit of power?
Watt, W
State the equation relating energy and efficiency.
Efficiency =
Useful Energy Output / Total Energy Input
State the equation relating power and efficiency.
Efficiency =
Useful Power Output / Total Power Input
What is the unit of efficiency?
Efficiency is a ratio and so doesn’t have an associated unit.
What is a moment?
A moment is the turning effect of a force.
State the equation used to calculate the moment of a force.
Moment of a Force = Force × Distance
What distance must be used when calculating a moment?
The perpendicular distance between the line of action of the force and the axis of rotation.
What is the unit of a moment?
Nm
What is the principle of moments?
For an object to be in equilibrium, the sum of the clockwise moments about a point must be equal to the sum of the anticlockwise moments.
What is an object’s centre of gravity?
The single point through which the object’s entire weight can be said to act.
How would you carry out an experiment working out the centre of gravity of an object
Punch 3 holes in each corner of the object.
Attach a hanging mass to a needle and put it in a bung which is being held by a clamp stand.
Draw a line from which the string/hanging mass goes over. Repeat for each hole. The point where all the lines cross is the centre of gravity
What will occur if the line of action an object’s centre of gravity lies outside its base?
The object’s weight will produce a resultant moment and so if is unsupported, the object may topple.
What is an elastic and an inelastic collision
Elastic- all kinetic energy and momentum is conserved
Inelastic - some energy and momentum is lost
