Forces 4 - speed/velocity/acceleration/displacement Flashcards
What does distance tell us, what doesn’t it tell us
Distance is how far an object has moved.
Distance does not involve direction (doesn’t say anything about the direction the car moved in only the distance it travelled
Explain why distance is a scalar quantitiy
Distance has magnitude but no direction therefore distance is a scalar quantity
Define displacement
Displacement includes both the distance an object moves,
measured in a straight line from the start point to the finish point
and the direction of that straight line
Explain why displacement is a vector quantity
Displacement includes both magnitude and direction THEREFORE displacement is a vector quantity
Give an example of a displacement measurement
380m EAST
Define speed
The distance an object has travelled in a given time
Equation that links speed, distance and time
Speed = Distance/Time
speed - m/s or km/h
distance - metres or km
time - s or hours
Explain why speed is a scalar quantity
Speed has magnitude but no direction therefore speed is a scalar quantity
State the typical speeds of:
walking
running
cycling
car
train
plane
speed of sound in air
Typical values may be taken as:
walking ̴ 1.5 m/s
running ̴ 3 m/s
cycling ̴ 6 m/s
car - approx. 13m/s
train - approx. 50m/s
plane - approx. 250m/s
speed of sound in air = 330m/s
the speed of sound can vary - (sound travels faster on warmer days than cooler ones)
State the factors which can affect the speed at which a person can walk, run or cycle
The speed at which a person can walk, run or cycle depends on
many factors including:
age, terrain (people move more rapidly on flat ground rather than moving uphill) , fitness and distance travelled
What types of speed varies
It is not only moving objects that have varying speed. The speed of
sound and the speed of the wind also vary
Define velocity
The velocity of an object is its speed in a given direction
State what we are saying speed or velocity
20m/s
20m/s south
20 m/s - stating speed
20m/s south - stating velocity
Explain why velocity is a vector quantity
Velocity includes both magnitude and direction, therefore velocity is a vector quanity
Equation for velocity
Same for speed
v = s/t
v - velocity
s - distance
t -time
A person walks in a straight line from point A to point B covering a distance of 50m
This takes 40s
Calculate the person’s velocity
v = s/t
v=50/40 = 1.25m/s south (the person is south)
Explain why the velocity of the car is constantly changing even though a car is travelling at a constant speed in a circle
Even though the car is moving with a constant speed, its direction is constantly changing, therefore its velocity is constantly changing
(if an object moves at a constant speed in a circle then its velocity is constantly changing even though its speed is constant)
How can the distance be represented if an object moves along a straight line
If an object moves along a straight line, the distance travelled can
be represented by a distance–time graph.
How can be speed of an object be calculated using a distance-time graph
The speed of an object can be calculated from the gradient of its
distance–time graph
How can the speed at any particular time be determined for an accelerating object
If an object is accelerating, its speed at any particular time
can be determined by drawing a tangent and measuring the
gradient of the distance–time graph at that time.
A person walked 100m in a straight line in 100 s
Then stopped for 40 seconds and then walked another 70 m in 50 seconds
What does an upward sloping curve tell us in a distance-time graph
This tells us that the object is constantly increasing in speed (accelerating)
How to know the speed at 100s
Place a dot on the line - 100 s
draw a tangent to the line
work out gradient of the line
1.75 m/s
What does these lines show:
straight line
flat line
steeper straight line
line going downwards
curve - upward/levelling off
straight line - object travelling at a constant speed
flat - object is stationary
steepening curve - This tells us that the object is constantly increasing in speed (accelerating)
curve levelling off - object is constantly decreasing in speed (decelerating)
line going backwards - the person is going back to their start point, faster at a constant speed
Explain why acceleration is a vector quantity
Velocity is a vector quantity as it has both magnitude and direction
The acceleration of an object is the change in its velocity over a given time
therefore acceleration is a vector quantity
Define acceleration
The acceleration of an object is the change in its velocity over a given time
therefore acceleration is a vector quantity
state the equation that links acceleration, change in velocity, time
a = ∆ v/t
acceleration = change in velocity/time
a = v - u /t
a = m/s^2
v & u = m/s
time in seconds
A car accelerated at 1m/s^2 for 20s
what does this mean
The car increased its velocity by 1m/s every second over a 20 second period
What does the gradient of a velocity-time graph tell us
The gradient of a velocity-time graph represents the acceleration
What does a flat line in a velocity-time graph represent
when gradient = 0
A flat line/horizontal line shows us that the object is travelling at a constant velocity
What does an upward and downward sloping/negative acceleration line represent in a velocity-time graph
An upward sloping line shows that the object is accelerating
A downward sloping line shows that the object is decelerating
What does a curved line indicate in a velocity-time graph
A curved gradient indicates that the object is either accelerating or decelerating at a non-uniform rate
How to calculate the distance travelled in a velocity-time graph
The total area under the graph tells us the distance travelled in a specific direction (displacement)
distance travelled = area under the graph
or
distance travelled - area under graph (calculated by counting squares)
e.g. 20 squares
each square has an area of 250
20 x 250 = total displacement of 5000 m
equation that links velocity, displacement and time
v = s/t
velocity = distance travelled in a given direction / time taken
velocity = displacement / time taken
velocity, v in m/s
displacement, s in s
time in s
