Topic 2 - Force And Momentum Flashcards
What is a scalar quantity?
A quantity that only has a magnitude
A quantity that doesn’t have direction
What is a vector quantity?
A quantity that has both magnitude and direction
How can a vector quantity be represented?
Using vector arrows
How do vector arrows represent vectors?
The length of the arrow represents the magnitude
The arrow points in the associated direction
Give three examples of vector quantities
Velocity
Displacement
Force
Give 6 examples of scalar quantities
Temperature Time Mass Speed Distance Energy
What is velocity?
The speed of an object in a specific direction
On a distance/time graph, what value does the gradient of the line represent?
The speed
On a displacement/time graph, what value does the gradient of the line represent?
The velocity
What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?
Draw a tangent to the curve at the required time
Calculate the gradient of the tangent
State the equation for the average acceleration of an object
Acceleration = change in velocity/time taken
How can the distance travelled by an object be calculated from a velocity -time graph?
By the area under the graph
On a velocity time graph, what does the gradient of the graph represent?
The acceleration
State the typical value for the speed of sound
330m/s
What is the typical human walking speed?
1.5m/s
What Is thesypical value for human running speed?
3m/s
What is a typical value for human cycling speed?
6m/s
What is the approx. Value for gravity on earth?
10m/s^2
What is the name given to the single force that is equable to all the other forces acting on a given object?
The resultant force
State Newton’s first law for a stationary object
If the resultant force on a stationary object is 0, the object will remain at rest
State Newton’s first law for a moving object
If the resultant force on a moving object is 0, the object will remain at constant velocity
State the defining equation for Newton’s second law
Resultant force = mass x acceleration
State Newton’s second law in words
An objects acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
What is weight?
The force that acts on an object due to gravity and the object’s mass
What quantities does weight depend on?
The object’s mass
The gravitational field strength
What is the unit used for weight?
Newton
What is the unit used for gravitational field strength?
N/kg
What piece of equit,ent can be used to measure an object’s weight?
A calibrated spring-balance or Newton meter
When can an object travelling at a constant speed not have constant velocity?
When it is changing direction, for example moving in a circle
Why does an object travelling at a constant speed in a circle not have a constant velocity?
Velocity can only be constant I’d the direction is constant
In circular motion, the direction is continuously changing
So velocity is constantly changing
What is the resultant force that acts on an object moving in a circle called, and in which direction does it act?
Centripetal force
Towards the centre of the circle
What is inertial mass?
A measure of how difficult it is to chang a given object’s velocity
State Newton’s third law
Whenever two objects interact, the forces that they exert on each other are always equal and opposite
State the equation for momentum
Mass x velocity
What is the unit used for momentum?
Kim/s
Kilogram metres per second
In a closed system, what can be said about the momentum before and after a collision?
They are equal
State the equation for change in momentum
Force x time
How can you measure human reaction times?
Using the ruler drop test
What is the regular drop test?
Person A and B hold each end of a ruler with the 0cm mark at the bottom
Person A drops the ruler without telling person B
Person B catches it
The distance travelled corresponds to their reaction time
Why is it important that the 0cm mark is at the bottom?
So you can see the distance directly without having to calculate it; otherwise a zero error would need to be accounted for
What is the stopping distance of a vehicle equal to?
The sum of the thinking distance and braking distance
For a given braking distance, if the vehicle’s speed is increased, what can be said about its stopping distance?
The stopping distance is increased with an increase in speed
Give a typical range of values or human reaction time
0.2 seconds - 0.9 seconds
Give four factors which can affect a driver’s reaction time
Tiredness
Drugs
Alcohol
Distractions
Give two factors which may affect braking distance
Condition of the car (brakes)
Weather conditions
Describe the energy transfers that take place when a car applies its brakes
Work is done by the friction force between the brakes and wheel
Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs
To stop a car in a given distance, if it’s velocity is increased, what must happen to the braking force applied?
It must also be increased
State two consequences of a vehicle undergoing very large decelerations
Loss of control of the vehicle
Kinetic energy converted to heat is very high causing brakes to overheat
