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.