Mechanics (2) Flashcards
What are the kinematic equations of motion used for?
To describe any object moving with constant acceleration
These equations are often referred to as the ‘suvat’ equations.
What does ‘s’ represent in the SUVAT equations?
Displacement (m)
What does ‘u’ represent in the SUVAT equations?
Initial velocity (m s−1)
What does ‘v’ represent in the SUVAT equations?
Final velocity (m s−1)
What does ‘a’ represent in the SUVAT equations?
Acceleration (m s−2)
What does ‘t’ represent in the SUVAT equations?
Time interval (s)
Which variables in the SUVAT equations are vector quantities?
s, u, v, a
This means they can be positive or negative depending on their direction.
When are the SUVAT equations applicable?
When acceleration is constant, but not zero
What indicates constant acceleration in a problem statement?
Explicit statement of ‘constantly accelerating’ or ‘constantly decelerating’
What condition might indicate constant acceleration in freefall?
‘Air resistance can be ignored’ or ‘air resistance is negligible’
What is the relationship between force and acceleration as described by F = ma?
Constant force leads to constant acceleration
What is the constant acceleration of objects in freefall?
9.81 m s−2
What value must be included in calculations when an object is slowing down?
A negative value for acceleration
What acceleration do objects thrown upwards experience?
Negative acceleration
They slow down as they ascend and reach a final velocity of zero at the top of their path.
What are the three types of graphs used to represent motion?
Displacement-time graphs, velocity-time graphs, acceleration-time graphs
What does the term ‘displacement-time’ signify in graph naming?
‘Displacement on the y-axis and time on the x-axis’
What does the slope of a displacement-time graph equal?
Velocity
What does a straight (diagonal) slope on a displacement-time graph represent?
A constant velocity
What does a curved slope on a displacement-time graph represent?
An acceleration
What does a positive slope on a displacement-time graph represent?
Motion in the positive direction
What does a negative slope on a displacement-time graph represent?
Motion in the negative direction
What does a zero slope (horizontal line) on a displacement-time graph indicate?
A state of rest
What does the slope of a velocity-time graph equal?
Acceleration
What does a straight line on a velocity-time graph represent?
Uniform acceleration
What does a curved line on a velocity-time graph represent?
Non-uniform acceleration
What does a positive slope on a velocity-time graph represent?
An increase in velocity in the positive direction
What does a negative slope on a velocity-time graph represent?
An increase in velocity in the negative direction
What does a zero slope (horizontal line) on a velocity-time graph indicate?
Motion with constant velocity
What does the area under the curve on a velocity-time graph equal?
Displacement or distance travelled
What does a zero slope (horizontal line) on an acceleration-time graph represent?
An object undergoing constant acceleration
What does the area under the curve on an acceleration-time graph equal?
The change in velocity
What is the significance of the steepness of the slope on an acceleration-time graph?
Meaningless
What are the two types of quantities?
Scalar and vector
Define a scalar quantity.
A quantity that has magnitude but not direction
Give an example of a scalar quantity.
Mass
Define a vector quantity.
A quantity that has both magnitude and direction
Give an example of a vector quantity.
Weight
What is distance?
A measure of how far an object has travelled, regardless of direction
Is distance a scalar or vector quantity?
Scalar
What is displacement?
A measure of how far it is between two points in space, including the direction
Is displacement a scalar or vector quantity?
Vector
How does distance differ from displacement?
Distance is total length of the path taken; displacement is the straight line between two points
What is speed?
A measure of the distance travelled by an object per unit time, regardless of direction
Is speed a scalar or vector quantity?
Scalar
What is velocity?
A measure of the displacement of an object per unit time, including the direction
Is velocity a scalar or vector quantity?
Vector
True or False: An object can have constant speed but changing velocity.
True
What does the arrow in vector notation indicate?
That the quantity has a direction, not an actual direction
How can vectors be combined?
Vectors can be combined by adding or subtracting them to produce the resultant vector.
What is another name for the resultant vector?
The net vector
What are the two methods used to add vectors
Calculation (for perpendicular vectors) and Scale Drawing (for non-perpendicular vectors)
What are the two methods used to combine vectors in a scale diagram?
The triangle method and the parallelogram method.
How do you combine vectors using the triangle method?
- Link the vectors head-to-tail.
- The resultant vector is formed by connecting the tail of the first vector to the head of the second vector.
How do you combine vectors using the parallelogram method
- Link the vectors tail-to-tail.
- Complete the resulting parallelogram.
- The resultant vector is the diagonal of the parallelogram.
What are the two steps for combining vectors by calculation?
- Finding the direction of the resultant using trigonometry.
- Finding the magnitude of the resultant using Pythagoras’ theorem.
How is the direction of the resultant vector determined?
The direction is found from the angle it makes with the horizontal or vertical.
What theorem is used to find the magnitude of the resultant vector?
Pythagoras’ theorem is used.
What are the two main considerations for solving projectile motion problems?
Constant velocity in the horizontal direction.
Constant acceleration in the perpendicular direction.
What is the only force acting on a projectile after it has been released?
Gravity
How does velocity behave in the horizontal direction for a projectile?
It remains constant because there are no horizontal forces
How is each force represented in a free-body diagram?
As a vector arrow that:
- Is scaled to the force’s magnitude.
- Points in the direction of the force.
- Is labeled with the force’s name or symbol.
What are the three rules for drawing a free-body diagram?
- Draw a point at the center of mass of the body.
- Draw the body free from contact with other objects.
- Draw forces using correctly oriented and proportional vector arrows.
What does it mean if an object is considered an extended but rigid body?
All parts of the object remain in the same position relative to each other when it moves.
What does Newton’s First Law state?
A body will remain at rest or move with constant velocity unless acted on by a resultant force.
What happens if the forces acting on an object are balanced?
The resultant force is zero, and the object’s velocity remains constant.
How can you determine if the forces on an object are balanced?
Forces to the left = Forces to the right
Forces up = Forces down
What does Newton’s Second Law state?
The acceleration of an object with constant mass is directly proportional to the resultant force on it.
What happens when a body experiences an unbalanced force?
It experiences a resultant force, leading to acceleration or deceleration.
What equation represents Newton’s Second Law?
ΣF = ma (where ΣF is the sum of forces acting on the object).
Why do moving objects usually experience a resultant force?
Because of friction and drag forces acting against motion.
What is terminal velocity?
The maximum velocity an object can reach when the forces in the direction of motion are balanced by the forces opposing motion.
What does “terminal” mean in “terminal velocity”?
It means “final”—no further increase in velocity occurs.
When does an object reach terminal velocity?
When the drag forces become equal to the driving force.
What is weight?
The force a body experiences due to being in a gravitational field.
What equation is used to calculate weight?
W=mg
What is gravitational field strength?
The force per kilogram acting on an object in a gravitational field.
What equation is used to calculate gravitational field strength?
g=F/m
What is freefall?
When an object falls under the influence of gravity alone, with no other forces acting on it (ignoring drag).
How does mass affect freefall acceleration?
It doesn’t— all objects fall with the same acceleration regardless of mass or weight.
What does Newton’s Third Law state?
Whenever two bodies interact, the forces they exert on each other are equal in size, act in opposite directions, and are of the same type.
How do forces always arise according to Newton’s Third Law?
In pairs—if object A exerts a force on object B, then object B exerts an equal and opposite force on object A.
What must be true about Newton’s Third Law force pairs?
They must be of the same type (e.g., gravitational, normal contact, frictional).
How does Newton’s Third Law apply to gravity?
If Earth pulls on an object with a gravitational force, the object pulls back on Earth with an equal and opposite gravitational force.
Equation for momentum
p=m/v
Is momentum a scalar or vector quantity?
Vector
SI unit for momentum
Kilogram meter per second
What does the principle of conservation of momentum state?
In a closed system, the total momentum before an event is equal to the total momentum after the event.
Under what conditions is momentum conserved?
Momentum is always conserved in collisions where no external forces act.
What is the general equation for momentum conservation in a collision?
Total momentum before a collision = Total momentum after a collision
Why can a system have an overall momentum of 0?
Because momentum is a vector quantity, so objects moving in opposite directions can cancel each other out.
What is the equation for total momentum after the collision?
(M × V) – (m × v), where:
M moves with velocity V
m moves with velocity -v (since it changes direction)
How does Newton’s Third Law apply to collisions?
When two objects collide, both experience equal and opposite forces, causing one to speed up (gain momentum) and the other to slow down (lose momentum).
Why do colliding objects not necessarily have equal accelerations?
Because acceleration depends on both force and mass, as stated in Newton’s Second Law (F=ma).
What is a moment?
A moment is the turning effect of a force
When do moments occur?
When forces cause objects to rotate about a pivot.
What is the equation for calculating a moment?
Force (N) × Perpendicular distance from the pivot (m)
What is the SI unit of a moment?
Newton metres (N·m).
How does a door demonstrate moments?
The door handle is placed far from the hinge (pivot) to maximize the distance, increasing the moment for a given force.
What is the centre of gravity?
The point through which all the weight of an object can be considered to act.
Where is the centre of gravity of a uniform regular solid?
At its geometric centre.
Where is the centre of gravity of a sphere?
At the exact centre of the sphere.
How does the position of the centre of gravity affect stability?
An object is stable when its centre of gravity lies above its base.
What does the principle of moments state?
For a system to be in equilibrium, the sum of clockwise moments about a point must equal the sum of anticlockwise moments about the same point.
What is the definition of work?
The amount of energy transferred when an external force causes an object to move over a certain distance.
When is work done?
Work is done when a force is applied to move an object over a distance.
What is the equation for work done when force is parallel to displacement?
W=Force x displacement
How does work done relate to energy?
Work is a transfer of energy; if force acts in the direction of motion, the object gains energy, and if the force acts against motion, the object loses energy.
How do you determine whether to use cosine or sine?
Use cosine when the angle is between the force and the horizontal.
Use sine when the angle is between the force and the vertical.
What happens when you push a block along a rough surface?
Work is done against friction, converting energy into kinetic energy, heat, and sound.
What equations to use to derive ke=mv^2/2
w=f*d, f=ma, v^2=u^2+2as
What is kinetic energy?
Kinetic energy (Ek or KE) is the energy an object has due to its motion (or velocity).
What happens to an object’s kinetic energy as it falls?
As an object falls, it gains kinetic energy because it is gaining speed.
From where does the kinetic energy come when an object is falling?
The kinetic energy is transferred from the gravitational potential energy that the object is losing.
What is gravitational potential energy?
Gravitational potential energy (Ep or GPE) is the energy stored in a mass due to its position in a gravitational field.
What happens to gravitational potential energy when a mass is lifted?
The mass gains gravitational potential energy (converted from other forms of energy).
What is the reference point for gravitational potential energy near Earth’s surface?
The potential energy at ground level (Earth’s surface) is taken to be equal to 0.
Are energy transfers 100% efficient in real-life situations?
No, there are always some energy losses from the system.
What are common causes of energy loss in a system? (3)
Friction, air resistance, and thermal energy dissipation.
What are common examples of energy exchanges between GPE and KE? (3)
- A swinging pendulum
- Objects in free fall
- Sports like skiing or skydiving, where gravity causes motion with minimal drag forces
How can energy conservation be used to find the final velocity of a moving object?
By equating initial gravitational potential energy to final kinetic energy.
What is power
Power is the rate at which energy is transferred.
How is power related to work done?
Power is the rate of doing work, or the work done per unit time.
How can power be calculated using force and velocity?
P=Force x velocity
What is efficiency in a system?
Efficiency is a measure of how well energy is transferred in a system.
Does efficiency have units?
No, efficiency is a ratio and has no units.
