P1 - Motion Flashcards
Acceleration
The rate at which velocity changes
Acceleration formula
acceleration = (final velocity-initial velocity) /time
a = (v-u)/t
Deceleration
A decrease in speed
What does a velocity-time graph show?
A velocity-time graph shows how the velocity of a moving object varies with time
- if the object is moving at a constant acceleration/deceleration
- the magnitude of the acceleration / deceleration
Straight line (velocity-time graph)
represents constant speed
Slope of a line (velocity-time graph)
magnitude/rate of the acceleration
Velocity
the speed of an object in a particular direction
Velocity formula
Displacement / time
Steep slope (velocity-time graph)
A steep slope means large acceleration (or deceleration)
Gentle slope (velocity-time graph)
A gentle slope means small acceleration and small change in velocity
Downward slope (velocity-time graph)
decreasing velocity (deceleration)
Horizontal/flat line (velocity-time graph)
A flat line means the acceleration is zero - i.e. the object is moving with a constant velocity
Average speed
total distance / total time
Newton’s first law
Objects in motion tend to stay In motion. Objects at rest tend to stay at rest unless acted upon by an external force
Newton’s second law
The acceleration produced by a net force is directly proportional to the net force and inversely proportional to the mass of the object.
Force = Mass x Acceleration
Newton’s third law
For every action there is an equal and opposite reaction
When object A pushes on object B, object B will exert and equal and opposite force on object A
Centre of Mass
The point at which the mass of an object is thought to be concentrated
Equilibrium
A state of balance (usually between two forces)
Moment
The turning effect of a force about a pivot
Pivot
A fixed point that the object can rotate around
Moment formula
Moment(Nm) = Force(N) x perpendicular distance from pivot(m)
M = Fd
Give 3 examples of moments
- door handle
- wheel barrow
- seesaw
- shovel
- crowbar
Principle of moments
If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot
What condition must be met for an object to be in equilibrium?
- The forces on the object must be balanced
- There must be no resultant force
- The sum of clockwise moments on the object must equal the sum of anticlockwise moments
Finding the centre of mass for a symmetrical object
The centre of gravity is located at the point of symmetry (find all lines of symmetry, where they cross is the centre of mass)
Explain how we can find the centre of mass for irregular shapes (4 steps)
1) The irregular shape (a plane laminar) is suspended from a pivot and allowed to settle
2) A plumb line (lead weight) is then held next to the pivot and a pencil is used to draw a vertical line from the pivot (the centre of gravity must be somewhere on this line)
3) The process is then repeated, suspending the shape from two different points
4) The centre of gravity is located at the point where all three lines cross
Explain why we can find the centre of mass for irregular shapes
When an object is suspended from a point, the object will always settle so that its centre of gravity comes to rest below the pivoting point
Density
The mass per unit volume of a material
- It tells us how tightly matter is packed together
Volume
The amount of space an object takes up
Sinking
To move downward below the surface of a liquid
Float
Remaining suspended in a liquid
Regular object
Any object that has even sides and smooth edges
Irregular object
Materials that are uneven in shape
Solid
Definite shape and volume
Low density relation to mass
Objects made from low density materials typically have a low mass
High density relation to mass
Similarly sized objects made from high density materials have a high mass
When does an object float?
- If the upthrust on an object is equal to (or greater than) the object’s weight, then the object will float
- If it has a density less than the density of the fluid it is immersed in, the object will float
When does an object sink?
- If the upthrust is smaller than the weight then the object will sink
- If it has a density more than the density of the fluid it is immersed in, the object will sink
Density formula
Density(kg/m3) = mass(kg)/volume(m3)
p = m/V
Measuring the density of regular objects (3 steps)
1) Place the object on a digital balance and note down its mass
2) Use ruler, Vernier calipers or micrometer to measure the object’s dimensions (width, height, length, radius)
3) Repeat these measurements and take an average of these readings before calculating the density
Measuring the density of irregular objects (6 steps)
1) Place the object on a digital balance and note down its mass
2) Fill the eureka can with water up to a point just below the spout
3) Place an empty measuring cylinder below its spout
4) Carefully lower the object into the eureka can
5) Measure the volume of the displaced water in the measuring cylinder
6) Repeat these measurements and take an average before calculating the density
What is the theorem for measuring the density of irregular objects?
Archimedes principle (Eureka!)
Hooke’s law
When an elastic object is stretched it’s extension (x) is directly proportional to the force (F) applied to it
Elastic
An object which when stretched, it exerts a restoring force which tends to bring it back to its original length
Inelastic
Not elastic
Extension
Extension happens when an object increases in length
- The extension of the spring is determined by how much it has increased in length
Stiffness
A material’s resistance to deformation
Spring constant
A parameter that is a measure of a spring’s resistance to being compressed or stretched
How does the steepness of line on a force and extension effect the stiffness of a spring?
- Very steep (full force): stiff spring
- Quite steep (full force): softer spring
- Shallow (full force): even softer spring
Limit of proportionality
The limit beyond which, when a wire or spring is stretched, its extension is no longer proportional to the force that stretches it (Hooke’s law is no longer applied)
Hooke’s law formula
Force(N) = spring constant(N/m) x extension(m)
F=kx
How does the spring constant effect the extension?
k is measure of the stiffness of the spring or material. The higher the value of k the stiffer the spring. Materials with a high k need a large force to for a given extension.
Newton’s Second Law formula
Force(N) = mass(kg) x acceleration(m/s2)
Acceleration formula
acceleration = force/mass
Mass formula
Mass formula
mass = force/acceleration
Mass
Mass is a measure of the quantity of matter in an object at rest relative to the observer
Weight
Weight is a gravitational force on an object with mass
Pressure
The concentration of a force or the force per unit area
How does mass affect inertia?
Mass is the property of an object that resists change in motion
- greater the mass of an object, the more difficult it is to speed it up, slow it down, or change its direction
- greater inertia
Gravitational field strength
The force per unit mass acting on an object in a gravitational field
Formula for Weight
Weight(N) = mass(kg) x gravity(N/kg)
W = mg
Formula for mass (using gravity and weight)
Mass(kg) = Weight(N)/gravity(N/kg)
m = W/g
What is the approximate gravitational field strength of Earth?
9.8 N/kg
Formula for gravitational field strength
gravity = weight (N) / mass (kg)
g = W/m
Explain the pressure of a pin
It is pushed into the surface, rather than up towards the finger
- This is because the sharp point is more concentrated (a small area) creating a larger pressure towards the surface
Formula of Pressure
pressure(pa) =force(N)/area(m2)
P=F/A
How does the surface area affect pressure?
- If a force is spread over a large area it will result in a small pressure
- If it is spread over a small area it will result in a large pressure
What does pressure depend on (2)?
- How much force is applied
- How big (or small) the area is on which the force is applied
Force
A push or a pull that acts on an object due to the interaction with another object
Non-contact force
A force which acts at a distance, without any contact between bodies, due to the action of a field
Contact force
A force which acts between objects that are physically touching
Balanced force
Equal forces acting on an object in opposite directions
Unbalanced force
Forces that produce a nonzero net force, which changes an object’s motion
Force formula
Force = mass x acceleration
How can forces effect an object (3)?
- Changes in speed: forces can cause bodies to speed up or slow down
- Changes in direction: forces can cause bodies to change their direction of travel
- Changes in shape: forces can cause bodies to stretch, compress, or deform
List the non contact forces (3)
- Gravitational force
- Electrostatic force
- Magnetic force
List the contact forces (5)
- Friction
- Tension
- Air Resistance
- Normal force
- Upthrust
Electrostatic force
A force experienced by charged objects which can be attractive or repulsive
* For example, the attraction between a proton and an electron
Air resistance (drag)
The friction of the air on a moving object
Weight
The name given to the force of gravity on a mass
Thrust
The force causing an object to move (such as the force from a rocket engine)
Upthrust
The force of a fluid (such as water) pushing an object upwards (making it float)
Compression
Forces that act inward on an object, squeezing it
Tension
Force transmitted through a cable or a string when pulled on by forces acting on its opposite ends
Reaction force
Force acting in the opposite direction to the action force
Action force
The initial push or pull of one object on another object
Normal force
The force perpendicular to a surface that prevents an object from falling through the surface
Newtonmeter
A device to measure force
Free-body diagrams
Diagrams used to show the relative magnitude and direction of all forces acting upon an object
Resultant force (net force)
A resultant force is a single force that describes all of the forces operating on a body
How to calculate the resultant force?
Resultant forces can be calculated by adding or subtracting all of the forces acting on the object
- Forces working in opposite directions are subtracted from each other
- Forces working in the same direction are added together
Gradient
A rate of inclination in speed; a slope
Stationary (distance-time graph)
Non-changing distance (horizontal line to x axis)
Constant speed (distance-time graph)
Moving at a steady rate over time
Steep slope (distance-time graph)
Object is moving at a large speed
Shallow slope (distance-time graph)
object is moving at a small speed
What does the slope of a straight line represent (distance-time graph)?
The slope of the straight line represents the magnitude of the speed
What does the slope of a curved line represent (distance-time graph)?
The object is moving at a changing speed
Outwards curve (distance-time graph)
Gradually decreasing speed (decelerate)
Inwards curve (distance-time graph)
Gradually increasing speed (accelerate)
Gradient formula (distance-time graph)
rise/run (change in y axis/change in x axis)
Declining straight line (distance-time graph)
The object is moving closer to its starting position
Speed
The distance an object travels per unit of time
Distance
How far an object moves or the length between two objects
Metres
the measurement of distance (m)
Seconds
the measurement of time
Scalars
quantities that have only a magnitude (do not include direction)
Vectors
quantities that have both a magnitude and a direction
Give examples of vectors (name 3)
displacement, velocity, acceleration, force, momentum
Give examples of scalars (name 3)
distance, speed, time, mass, energy, power, work
Momentum formula
mass x velocity (p=mv)
Power
The rate at which work is done
Energy
The ability to do work or cause change
Displacement
Distance and direction of an object’s change in position from the starting point (final position - initial position)
Formula for speed
speed(m/s) = distance(m)/time(s)
Formula for distance
distance(m) = speed(m/s) x time(s)
Formula for time
time(s) = distance(m)/speed(m/s)
Micrometer
A micrometer is used as a piece of measuring instrument for making precise linear measurements
- it is very useful to determine some tiny dimensions such as thickness, diameter, and lengths of solid bodies
Accuracy
How close a value is to the known value
Percision
How close two measurements are to each other
Calipers
A pinching instrument used for determining the thickness of objects or the distance between surfaces
Error
The difference between the experimental value and the accepted value
Thimble
The lower measuring part of the micrometer which can help advance the spindle
Ammeters
measure the flow of current through a circuit
Voltmeters
measure voltage
Measuring cylinder
to measure the volume of a liquid
Analogue clocks
physically quantified portrayal of time (a watch)
Digital clocks
digitally / non-physical portrayal of time (smart phone)
How to measure the period of a pendulum? (3 steps)
1) Set up a pendulum using the clamp and stand. Use the G-clamp to fasten the bottom of the stand to the bench so that it does not fall over when the pendulum swings.
2) The period of a pendulum is the time for one complete swing. Swing the pendulum and measure its period. Repeat this three times for each length.
3) Repeat for five different lengths, recording your results in the table
Friction
A force that works in opposition to the motion of an object
- slows down the motion of the object
- energy is transferred to heat: rises temperature
Freefall
The law that in the absence of air resistance, all objects fall with the same acceleration
- The acceleration of free fall states that: for every second an object falls, its velocity will increase by 9.8 m/s
