Dynamics Flashcards
Define speed
Speed is the distance travelled by an object in a certain time
Define average speed
The total distance travelled divided by the total time taken
How do you calculate average speed?
To calculate the average speed of a journey we need to measure a distance and a time
Name 3 distance measuring equipments
Ruler,Trimble wheel, meter stick, measuring tape
Name 3 time measuring equipments
Stop watch, clock, stopclock
The relationship used to measure average speed is?
v = d/t (this will be written as d = vt on the relationship sheet)
where:
v = speed measured in metres per second (ms^-1)
d = distance measured in metres (m)
t = time measured in seconds (s)
What is instantaneous speed
Instantaneous speed is the speed of a moving object at any particular instant in time.
How do you measure instantaneous speed?
You need to measure the distance travelled in a very short time, this can be done by using a ruler to measure the length of an object and a light gate connected to a timer to measure the time it takes for the object to pass a fixed point
Define acceleration
Acceleration is the change in speed of a moving object per second
How to calculate acceleration?
Change speed/ time, as a formula this is written as a = v-u/ t
where:
a = acceleration measured in metres per second per second (ms^-2)
v = final speed measured in metres per second (ms^-1)
u = initial speed measured in metres per second (ms^-1)
t = time measured in seconds (s)
Explain deceleration
If an object is decelerating the final speed will be less than the initial speed, this means the change in speed will be negative and so will the anwser for a in the formula
In a speed time graph how can you find the acceleration
The acceleration in a speed time graph is the gradient of the line
How do you work out the distance travelled using a speed time graph
Calculate the are under the graph
What is friction
Friction is a force that acts in the opposite direction to an objects movement.
What does friction do?
It slows down or stops a moving object.
When does a frictional force occur
A frictional force always acts when two surfaces are rubbing against each other.
How can you decrease how much friction effects an object?
Lubricating surfaces (eg oiling)
Decreasing surface area
Smoothing surfaces
Streamlining the shape
What does the term “balanced forces” mean
Balanced Forces means the forces acting on an object are equal in size but act in opposite directions.
State Newton’s first law
An object at rest will remain at rest and an object in motion will remain in motion with a constant speed in a straight line unless acted on by an unbalanced force.
Why do things slow down if we don’t keep pushing them?
Because of friction
If you push something in space what happens and why
It keeps on moving at a constant speed for ever because there is no friction
State Newtons 2nd law
When an unbalanced force acts on an object it will accelerate. F = ma
where:
F = unbalanced force measured in newtons (N)
m = mass measured in kilograms (kg)
a = acceleration measured in metres per second per second (ms^-2)
What is the definition of mass in physics
Mass is a measure of how much matter there is in a substance
Measured in kilograms (kg)
What is the definition of weight in physics
Weight is the force due to gravioty acting on a mass.
Weight is measured in Newtons (N) and it is a force.
What causes the weight of an object
The pull of gravity
What is gravitational field strength
The force gravity applie to a mass of 1 kg
What is the gravitational field strength on earth.
9.8 N kg^-1
What is the formula for weight
W = mg
where:
W = weight measured in newtons (N)
m = mass measured in kilograms (kg)
g = gravitational field strength measured in newtons per kilogram (N kg^-1)
State Newtons 3rd law
If object A exerts an action force on object B, object B will exert an equal and opposite reaction force on A.
What is freefall?
Freefall is any motion where gravity is the only force acting upon it.
Newton’s Laws apply to freefall.
Because this is an unbalanced force the object will keep accelerating (at 9.8 ms^-2 on earth)
What is terminal velocity?
Terminal velocity is the constant vertical speed reached by a falling object when the forces acting on it are balanced.
