Force and Motion Flashcards
What is a scalar quantity?
A quantity that only has a magnitude and that isn’t direction dependent
What is a vector quantity?
A quantity that has both magnitude and an associated direction
How can a vector quantity be represented?
Using vector arrows
How do vector arrows represent vectors?
The length of arrow represents the magnitude and the arrow points in the associated direction
What are some examples of vector quantities?
Velocity, displacement and force
What are some examples of scalar quantities?
Temperature, time, mass, speed, distance and energy
What is velocity?
The speed of an object in a specific direction
What is the equation of speed?
Average speed = distance / time
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 and calculate the gradient of the tangent
What is the equation for the average acceleration of an object?
Acceleration = change in velocity / time taken
What is the equation relating to final velocity with initial velocity, displacement and acceleration?
v^2 = u^2 + 2as
How can the distance travelled by an object be calculated from a velocity-time graph?
It’s equal to the area under the graph
On a velocity-time graph what does the gradient of the graph represent?
The acceleration
What is the typical value for the speed of sound?
330 m/s
What is the typical value for human walking speed?
1.5 m/s
What is the typical value for human running speed?
3 m/s
What is the typical value for human cycling speed?
6 m/s
What is the approximate value for the acceleration of an object in free fall under gravity near the Earths surface?
10 m/s^2
When can an object travelling at a constant speed not have a constant velocity?
When the object is changing direction
Why does an object travelling at a constant speed in a circle not have a constant velocity?
Speed is a scalar quantity and velocity is a vector quantity which means it can only be constant if the direction is constant, in circular motion the direction is continuously changing which means velocity is constantly changing
What is the resultant force that acts on an object moving in a circle called?
Centripetal force, acts towards the centre of the circle
What is inertial mass?
A measure of how difficult it’s to change a given objects velocity and the ration of force over acceleration
What is Newton’s third law?
When two object interact, the forces that they exert on each other are always equal and opposite
What is the equation used to calculate an object’s momentum?
Momentum = mass x velocity
What is the unit used for momentum?
kgm/s (kilogram metres per second)
In a closed system, what can be said about the momentum before and after a collision?
The total momentum before and after are equal
What is the equation of the change in momentum
Force x time = change in momentum
How can you measure human reaction times?
Using the ruler drop test, person A and B hold each end of a ruler with the 0 cm mark at the bottom, person A drops the ruler without telling person B, person B catches it and the distance travelled corresponds to their reaction time
Why is it important that the 0cm mark is at the bottom of the ruler drop test?
So you can obtain 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 thinking and braking distance
If the vehicles speed is increased, what can be said about its stopping distance?
The stopping distance is increased with an increase in speed
What are the typical ranges of values for human reaction time?
0.2 - 0.9 seconds
What are three factors which can affect a drivers reaction time?
Tiredness, drugs and alcohol
What are two factors which may affect braking distance?
Wet/icy road conditions and poor tyre/brake conditions
What are the energy transfer ps that take place when a car applies its brakes?
Work is done by the friction force between the brake and wheel and kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs
If velocity is increased, what must must happen to the braking force applied?
The braking force must also be increased
What are the consequences of a vehicle undergoing very large decelerations?
Kinetic energy converted to heat is very high causing brakes to overheat and loss of control of the vehicle
What is the name given to the single force that is equivalent to all the other forces acting on a given object?
The resultant force
What is Newton’s first law for a stationary objects?
If the resultant force on a stationary object is zero, the object will remain at rest
What is Newton’s first law for a moving object?
If the resultant force on a moving object is zero, the object will remain at constant velocity
What is the equation for Newton’s second law?
Resultant force = mass x acceleration
What is Newton’s second law in words?
An object’s 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 objects mass
What quantities does weight depend on?
The objects mass and the gravitational field strength at the given position in the field
What is the unit used for weight?
Newton
What is the unit used for gravitational field strength?
N/kg
What piece of equipment can be used to measure an objects weight?
A calibrated spring-balance or newton-meter
