Physics: Motion, Forces And Conservation Of Energy Flashcards
What do vector quantities have?
Magnitude (size) and direction
What do scalar quantities have?
Magnitude (size)
Two bikes are travelling in different directions. Would their velocity be different or the same?
Different, because they’re moving in different directions
What is distance? Scalar or vector?
How far an object has moved . Scalar.
What is displacement? Scalar or vector?
Distance and direction in a straight line for a starting point to finishing point. Vector
Someone walks 5m north then 5m south. What is their distance? What is their displacement?
Distance = 10m, displacement = 0m
What is speed? Scalar or vector?
How fast you’re going. scalar.
What is velocity? Scalar or vector?
How fast you’re going (speed) in a given direction
Give an example of velocity
30mph north
If something has a constant speed but changing velocity, what is it doing?
Traveling at the same speed but changing direction
For an object travelling at a constant speed, what is the formula?
(Average) speed = distance traveled/ time
Units for distance travelled?
M
Units of (average) speed?
m/s
Units for time?
s
What is the typical average speed for walking? Give answer in m/S and km/h
1.4m/S, 5km/h
What is the typical average speed for running? Give answer in m/S and km/h
3M/s, 11km/h
What is the typical average speed for cycling? Give answer in m/S and km/h
5.5m/S, 20km/h
What is the typical average speed for cars in a built up area? Give answer in m/S and km/h
13m/S, 47km/h
What is the typical average speed for cars on a motorway? Give answer in m/S and km/h
31m/S, 112km/h
What is the typical average speed for trains? Give answer in m/S and km/h
55m/S, 200km/h
What is the typical average speed for aeroplanes? Give answer in m/S and km/h
250m/S, 900km/h
What is the typical average speed for ferries? Give answer in m/S and km/h
15m/S, 54km/h
What is the typical average speed for wind speed? Give answer in m/S
5-20m/S
What is the typical average speed for speed of sound in air? Give answer in m/S
340m/S
What is uniform acceleration?
Speeding up or slowing down at a constant rate
What is acceleration? Two ways of saying this.
How quickly you’re speeding up, change in velocity in a certain amount of time
What is the formula for average acceleration of an object?
Acceleration = (change in velocity)/time
How do you work out initial velocity?
Final velocity - Initial velocity
What are the units for acceleration?
m/s^2
What are the units for change in velocity?
m/S
Something is slowing down. What will we know about the change in velocity?
It’ll be negative
A car is travelling 15m/S, when it collides with a tree and comes to a stop. Estimate the deceleration of the car.
1) estimate how long it would take the car to stop.
Car comes to a stop in ~1s
2) put this number into acceleration equation
a=(v-u)/t
a=(0-15)/1
3) car has slowed down, acceleration is negative
=-15m/s^2
Deceleration = 15m/s^2
What can we say about acceleration due to gravity in objects that are in a free fall?
Acceleration due to gravity is uniform/constant
What is acceleration due to gravity equal to? What else does ‘‘tis value represent?
Roughly 10m/s^2
Gravitational field strength
What is the equation for uniform acceleration?
Final velocity - initial velocity = 2 x acceleration x distance
V^2-u^2=2xaxx
A van travelling at 23m/S starts decelerating uniformly at 2.0m/s^2 as it heads towards a built up area 112m away. What will it’s speed be when it reaches the built up area?
1) rearrange equation so v^2 is on one side
V^2=u^2+ (2 x a x X)
2) put in numbers - a is negative due to declaration
V^2 = 23^2 + (2 x -2.0 x 112)
=81
3) Square root the whole thing
V= square root of 81 = 9m/S
What do distance/time graphs tell you?
How far something has travelled + speed of an object
What do the different parts of a distance/time graph show?
The motion of the object
What does the gradient (slope) at any point on a distance time graph tell us?
The speed of an object
If a line is flat on a distance time graph, what does it show?
It has stopped
If a line is steep on a distance time graph, what does it show?
Going faster
If a line is curved on a distance time graph, what does it show?
Acceleration
If a curve is getting steeper on a distance time graph, what does it show?
Speeding up
If a curve is levelling off (flattening) on a distance time graph, what does it show?
Slowing down
If the distance time graph is a straight line, what is the speed?
Equal to the gradient of the line
What is the equation for gradient of a line?
Speed=gradient= change in vertical/change in horizontal
If a distance/time graph is curved, how do we find the speed at a certain time?
Draw a tangent to the curve at that point, and then find the gradient of the tangent
What is a tangent?
A line that is parallel to the curve at that point
How do we calculate average sheep of an object when it has a non uniform motion (accelerating)?
Divide total distance traveled by the time it takes to travel that distance.
Sketch a distance/time graph for an object that initially accelerates, then travels at a constant speed, then decelerates to a stop
Continuous line that initially curves upward, which curves downward at the end until it becomes horizontal. Straight middle section.
What kind of gradient can velocity/time graphs have?
Positive or negative gradient
What is shown on a velocity/time graph?
How an objects velocity changes over time
What does the gradient on a line on a velocity time graph tell us?
Acceleration, since acceleration=change in velocity/time
On a velocity time graph, what do flat sections represent?
A steady speed
What can we say about steepness the velocity/time graph in relation to acceleration.
Steeper the graph, the greater the acceleration or deceleration
On a velocity time graph, what do uphill ( / ) sections show?
Acceleration
On a velocity time graph, what do downhill ( \ ) sections represent?
Deceleration
On a velocity time graph, what does a curve represent?
Changing acceleration
If a velocity/time graph is curved, how can we work out the acceleration at that point?
Use a tangent to the curve
Where on a velocity time graph is the distance travelled represented?
The area under the graph
What is the area under any section of a velocity/time graph (or all of it) equal to?
Distance travelled in that time interval
A velocity/time graph has bits where the accelerations constant. How can we work out the area under the graph?
Split it into rectangles and triangles
A stationary car starts accelerating increasingly for 10s until it reaches a speed of 20m/S. It travels at this speed for 20 seconds until the driver sees a hazard and brakes. He decelerates uniformly, coming to a stop 4s after braking. Draw the velocity/time graph for this journey. Using the graph, calculate the deceleration of the car when it breaks.
Upward curved acceleration line to 20m/S, straight line representing steady speed, straight line representing uniform deceleration a(cceleration)=gradient of the line =change in vertical/change in horizontal =(0-20)/(34-30) =-20/4=-5m/s^2 Deceleration = 5m/s^2
What is the simple way of putting Newton’s first law?
A resultant force is needed to make something start moving, speed up or slow down.
What happens to a stationary object of the resultant force on it is zero?
Object will remain stationary
What happens to a moving object of the resultant force on it is zero?
It’ll carry on moving at the same velocity (same speed and direction)
What will a non-zero resultant force always do?
Produce acceleration or deceleration in the direction of the force
What are the five different forms acceleration of an object with a non zero resultant force acting on it can take?
Starting, stopping, speeding up, slowing down ad Changing direction
What is the simple way of putting Newton’s second law?
Acceleration is proportional to the resultant force