2.1 - Motion Flashcards
How do we calculate rate of movement (speed)
Speed = distance / time
V = d/t
What is velocity
When you include the direction in the information about the rate of movement of an object - this is velocity
It’s the rate of change of displacement - wher the distance in a particular direction is called the displacement
What’s displacement
The distance in a particular direction
How is velocity calculated
Velocity = displacement / time
V = s/t
Or v = little triangle s / little triangle t
What’s a vector
A quantity in which the direction must be stated is known
What’s a scalar quantity
If direction is not important - the measurement is referred to as a scalar quantity
How are vectors notated ? (Idk if it’s just the way the book does it or if it’s true irl lol)
Vector notation means that vectors are written in bold type to distinguish them from scalar variables
How is average speed calculated
Calculated by dividing the total distance for a journey by the total time for the journey - thus it averages Out the slower and faster parts off the journey and even includes stops
What’s acceleration
It’s defined as the rate of change of velocity, therefore it must include the direction in which the speed is changing and so acceleration is a vector quantity
How can we calculate acceleration
Change in velocity / time taken to change the velocity
a = (v - u)/ t
What is the vector nature of acceleration
If an object changes just the direction of its velocity, it’s accelerating whilst remaining at a constant speed
Similarly, deceleration represents a negative change in velocity and so could be quoted as a negative acceleration
What’s the greatest speed possible
No speed or velocity can ever be greater than the speed of light which is 3 x 10^8 m/s
If one calculates a speed higher than this, one must be wrong m8 ya idiet
Define speed
The rate of change in distance
Define velocity
The rate of change of displacement
Define displacement
The vector measurement of distance in a certain direction
Define a vector
A vector quantity must have both magnitude and direction
Define a scalar
A scalar quantity only has magnitude
Define average speed
Calculated by dividing the total distance for a journey by the total time for the journey
Define instantaneous speed
Is the speed at any particular instant in time on a journey, can be found from the gradient of the tangent to a distance time graph at that time
Define acceleration
Is the vector defined as the rate of change of velocity
How can a velocity time graph be generated
Can be produced from direct measurements of the velocity or generated from calculations made using a displacement time graph
What da difference with displacement and distance graphs against time
Displacement time graphs can have a decreasing displacement y value whereas a distance time graph y value can only increase !
What can we find out from displacement time graphs / distance graph
Simplest thing is how far an object has moved in a certain amount of time
A flat line bit means the object is stationary
The gradient tells us the speed - found from the ratio of change of y axis divided by x axis
- distance / time
Or displacement / time
What does a velocity time graph show
Shows the velocity of an object over time
For velocity we can also tell the direction with the y value being positive or negative
How can we calculate acceleration from a velocity time graph
We must divide a change in velocity by the corresponding time difference to find the gradient and so acceleration.
How can we calculate th distance travelled from a v-t graphs
We must calculate the areas from between the lines of the graph and axis
Add the areas to get total distance
How can we find the acceleration due to gravity by multiflash photography
Using multiflash photography technique, or a video recording that can be played back frame by frame - we can observe the falling motion of a small object such as a marble, we need to know the time between frames
From each image of the falling object, measure the distance it has fallen from the scale in the picture, a carefully drawn distance time graph will show a curve as the object accelerates, from the curve, take regular measurements of the gradient using tangents of the curve - making instantaneous speeds, plotting these speeds on a velocity time graph should show a straight line - as acceleration from gravity is constant. The gradient of line will be acceleration due to gravity
What do acceleration time graphs show
Shows how the acceleration of an object changes over time,
Curve will change as acceleration changes due to changes in air resistance etc
What happens if the distance time graph line is curved
It’s a changing velocity - so acceleration or deceleration is happening
Define a displacement time graph
A graph showing the positions visited on a journey - with displacement on the y axis and time on the x axis
Define a velocity time graph
A graph showing the velocities in a journey, with velocity on the y axis and time on x axis
What’s deceleration on a distance time graph line look like
Going into a n shape kind of
What does acceleration look like on a distance time graph look lik
Like a u - like the 2nd half of the u
What time of quantity are forces
Vectors
What does using vector addition tell us
We can add and subtract all forces to work out the resultant force
Add forces in the same direction and subtract if they are in opposite direction
How can we describe the resultant force
We can consider it as the single force that has the same effect as all the Individual forces combined
How can we calculate a resultant forces if they’re perpendicular
Use soh cah toa
Or Pythagoras if ya want babez 🙈
Trigonometry will determine angle / direction is the resultant
How should we state the angle of a resultant force from perpendicular forces
The angle should be stated as from the horizontal, and draw the angle on the triangle thing to clearly show the angle
How can we find out the resultant of 2 non perpendicular forces
We draw the forces on make a triangle some way and use trig
Check pg 21 or text book lolz
What’s the parallelogram rule FOR
finding the resultant of 2 non perpendicular forces or vectors by a scale drawing, draw vectors to scale, draw the same vectors to make a parrelogrsm (lol just check pg 22 to see) ,
Then draw a line joining 2 sides to make the longest possible line which will be the hypotenuse
- will be the diagonal across the parallelogram from the starting point
Omg wait what if there more than 2 vectors ?
Add 2 together and then add to another and another until, all have been added in yes
What are free body diagrams for
If we clarify what forces are acting on an object, it can be simpler to calculate how it will move - to do this be usually draw a free body diagram
The object is isolated and all the forces that act on it are drawn in at the points they act from ,
Other objects not drawn, only the effect these objects have on the original object you drawing free body diagram of - only the force from that object drawn on
Ya get me
Define the resultant force
It’s the total force (vector sum) acting on a body when all the forces acting are added together accounting for their directions
Define a free body diagram
A free body diagram of an object has the object isolated and all the forces that act on it are drawn in at points where they act, using arrows to represent the forces
How can forces affect an object
It may bend or rotate
When might an object bend when a force is applied
If the object is fjxed so it can’t rotate - it will bend
When might an object rotate
When a force is applied, an object does not start to move Along but instead rotate about a fixed pivot point
What is the moment of a force
The tendency to cause rotation is called the moment of a force
How do we calculate the moment of a force
Moment (Nm) = force (N) x perpendicular distance from the pivot to the line of action of the force (m)
M=fx
What direction will an object move when a force is applied
A body will turn in the direction of any net moment
What’s the principle of moments
The sum of the clockwise moments is equal to the sum of anti-clockwise moments when a body is in rotational equilibrium
What’s rotational equilibrium
This means the object will remain stationery or if it’s already rotating it will continue at the same speed in the same direction
The sum of all forces acting on the object is 0
What if there’s more than one moment in the same direction
Calculate individual moments and then add them together
What’s the centre of gravity
The weight of an object is caused by the gravitational attraction between the earth and each particle contained within the object. The sum of all these tiny weight forces appears to act from a single point in any object - the centre of gravity
How do the calculate the centre of gravity for a symmetrical object
We can calculate the centre of gravity as it must lie on every line of symmetry - the point of intersection is the centre of gravity
What’s the centre of gravity also equal to
The centre of mass - the point is identical for objects that are small compared to the size of the earth
How do we work out the centre of gravity for irregular shaped objects
It’s the point at which it’s weight appears to act on the object
Eg a Bunsen burner has a heavy base so the centre of gravity is low down near the concentration of mass as there will be greater attraction by the earths gravity to this large mass
How can we investigate finding the centre of mass of an irregular rod
We use the principle of moments, try balance the rod , if it’s a broom - it will be difficult to do thus exactly so we can use an alternative method, measure the mass of the rod then use a set of hanging masses on the rod to balance it more in the middle and then calculate the clockwise moment to the anti clockwise moment and then calculate the distamce and that’s the centre of gravity ? Pg 25
Define a body in equilibrium
It’s in equilibrium if there is a zero resultant force and zero resultant moment, it will have a zero acceleration
Define the principle of moments
States a body will be in equilibrium if the sum of clockwise moments acting on it is equal to the sum of the anti clockwise moments
Define the centre of gravity of an object
It’s the point through which the weight of the object appears to act
What is Newton’s first law of motion
If an object is stationary, there needs to be a resultant force to make it more. If the object is already moving, it will continue at the same speed in the same direction unless a resultant force acts on it.
If there is no resultant force on an object, either because no forces are acting on it or all the forces balance out - then the objects motion is unaffected
What is Newton’s second law of motion
This law tells us how much of an objects motion will be changed by a resultant force, for an object with constant mass, it’s usually written as
F = ma
(Resultant force = mass x acceleration)
How can we investigate Newton’s second law in an experiment
Set up an experiment with a data logger, laptop, light gates and a trolley in motion , change the masses that make trolley accelerate
Measure the acceleration- draw a graph if it’s a straight line this means this means acceleration is proportional to resultant force
You can do a graph of acceleration against 1/mass to show acceleration is inversely proportional to mass
Investigation demonstrates a = f/ m
- rearrangement of Newton’s second law
When can a graph be described as directly proportional
Y = mx + c
If c =0 , the line will pass through the origin it’s directly proportional
What are most types of physics relationships
Causal relationships - eg acceleration is caused by force
Rarely are they statistical correlation so describing a graph as having a positive correction may not be appropriate babes
Ooooo inaProPriaTE bEHavioUr
What is Newton’s third law of motion
When object a causes a force on another object b, then object b causes an equal force in the opposite direction to act upon object a,
Every force has an equal and opposite reaction force
Define simply Newton’s first law of motion
An object will remain at rest, or in a state of uniform motion, until acted upon by a resultant force
Define Newton’s second law of motion simply
If an objects mass is constant, the resultant force need to cause an acceleration is given by f = ma
Define Newton’s third law of motion simply
For every reaction, there is an equal and opposite reaction
What is kinematics
The study of the movement of objects, use equations known as SUVAT equations to find out details about the motion of objects accelerating in one direction
What is uniform motion
If an object has no resultant force acting on it then it does no accelerate - this is uniform motion
In this situation we involve only simply v = s/t equation
As velocity at the start is the same as the end
What are the variables of suvat equatjons
We can work out the variables for an object with constant acceleration
S - displacement U - initial velocity V - final velocity A - acceleration T - time
Tell me about finding a variable with suvat equations
Each equation has 4 variables, which means if we know the values of any 3 variables, we can find out the other 2
If an object is falling what variable do we already know
A = 9.81 due to gravity
a= g
Can we combine equations
Yes, substitute different variable equations in to work out stuff
Hol up what if there’s 2 equations I Could use
Use either lol we should get the same answer lol
Tell me suvat equation where distance is not used
V = u + at
Tell me suvat equation where acceleration not used
S = (u + v)/2 x t
Tell me about suvat equation not including final velocity
S = ut + 1/2at^2
Tell me about the suvat equation not including time
V^2 = u^2 + 2as
Can I use suvat equatjons if acceleration is changing?
NO NO NO NOOOO
How can we investigate finding the acceleration due to gravity by free fall
A system for timing the fall of an object under gravity can allow us to measure the acceleration due to gravity
Measure time to fall from a certain height, then alter the height and measure again
We can use suvat to work out the time and height and plot time against height, we can use a line of best fit to calculate gravity (a)
How can we reduce uncertainty from single measurements
A single measurement in any experiment is prone to uncertainty from random and systematic error, we can reduce these by
Taking many readings and plotting a graph which leads to much more reliable conclusions
Define kinematics
It’s the study of the description of the motion of objects
Define uniform motion
It’s the Motion when there is no acceleration
Velocity = displacement/time
What is resolving vectors or resolution
FIND the 2 vectors that make the overall vector that starts from the same point as the other 2
How can we resolve vectors
We need an angle, between either the vertical or horizontal component and then use trigonometry to split it up
We can also use a scale diagram
The pair of vectors must be right angles to each other
You can continue to resolve new vectors after working out 2, then work out vectors parallel and perpendicular and stuff Or something idk
Define resolution or resolving vectors
The determination of a pair of vectors at right angles to each other that sums to give the single vector they were resolved from
What motion to objects thrown or fired tend to have
A projectile motion
How do vectors acting at right angles act
They act INDEPENDENTLY consider them on their own, their combined effect can be calculated with vector addition but they can also be considered to act separately and at the same time - this would cause independant effects which themselves could be combined to see an overall effect
‘Physics is holistic’ - what this mean
You can apply any rule to all things. Physics is a set of rules to explain everything in the universe
What do we consider about the motion when an object has been thrown or whatever
We only consider the motion after the force projecting an object has finished
Eg if something fired from a cannon, after cannon fired ,air resistance is ignored - the only force acting considered is the objects weight
What happens when a object is thrown horizontally
When an object is projected horizontally, it will start off with zero vertical velocity, however gravity will act on it so that it’s motion will curve downwards, in a parabola shape
What’s different about a vertical component to horizontal
Horizontal had no accelerating force for. Gravity or anything so just use v = d/t to calculate things
Use suvat for vertical,
How can we recombine velocity components
Adding the vertical and horizontal components into their resultant using trig
Tell me about the trajectory of a vertical throw
If a ball goes up forward, at the highest point the vertical velocity is momentarily 0
A vertical upwards component of motion will have a symmetrical trajectory
Getting to the highest point will take half the time of the whole flight
Define a projectile
It’s a moving object on which the only force of significance acting is gravity. The trajectory is pre determined by its initial velocity
