P5 - Forces 3 Forces , Elasticity and Motion Flashcards
Explain the relationship between force applied and the extension of an elastic object
The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
What is meant by an inelastic (plastic) deformation ?
- A deformation which results in the object being permanently stretched
- The object doesn’t return to its original shape when the force is removed
State the equatiom relating force, spring constant and extension . Give appropriate units
Force = Spring Constant x Extension
Force (N) , Spring constant (N/m) , Extension (m)
What type of energy is stored in a spring when it is stretched ?
Elastic potential energy
What can extension be replaced with in the equation for spring force ?
Compression
Does a distance quantity require a specific direction ? i.e. is it a scalar or vector quantity
No specific direction is required so it is a scalar quantity
If an object moves 3 metres to the left and then 3 metres back to its initial position, what is the object’s total displacement?
• The object has zero displacement
• Displacement is a vector quantity so it also involves direction
• The object starts and ends at the same point
State a typical value for the speed of sound
330 m/s
What is a typical value for human walking speed ?
1.5 m/s
What is a typical value for human running speed ?
3m/s
What is a typical value for human cycling speed ?
6 m/s
State the equation linking distance , speed and time . Give appropriate units
Distance = speed x Time
Diatance (m) , Speed (m/s) , Time (s)
Why can an object travelling at a constant speed in a circle not have a constant velocity ?
• Speed is a scalar quantity
• 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
How can speed be calculated from a distance-time graph ?
The speed is equal to rhe gradient of the graph
What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?
- Drawing a tangent to the curve at the required time
- Calculating the gradient of the tangent
State the equation for the average acceleration of an object. Give appropiate units.
Acceleration = (Change in Velocity)/(Time Taken)
Acceleration (m/s^2), Velocity (m/s) , Time (s)
How can the distance travelled by an object be calculated from a velocity-time graph?
It is equal to the area under the graph
What can be said about the resultant force acting on an object when it is falling at terminal velocity?
- The resultant force is zero
- When at terminal velocity, the object is moving at a constant speed and so isn’t accelerating
State Newton’s first law for a stationary object
If the resultant force on a stationary object is zero, the object will remain at rest
State 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 (same speed in same direction)
What can be said about the braking forces and driving forces when a car is travelling at constant velocity ?
The braking forces are equal to the driving forces
If an object changes direction but remains at a constant speed , is there a resultant force ?
Since there is a change in direction , there is a change in velocity and so there must be a resulatant force
What is inertia ?
The tendency of an object to continue in the same state of motion
State the defining equation for Newton’s Second Law
Resultant force = Mass x Acceleration
F = ma
State 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 inertial mass ?
- A measure of how difficult it is to change a given object’s velocity
- The ratio of force over accelration
State Newton’s third law
Whenever two objects interact, the forces that they exert on each other are always equal and opposite
What is the stopping distance of a vehicle equal to ?
The sum of 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 for human reaction time
0.2 seconds - 0.9 seconds
Give three factors which can affect a drivers reaction time
- Tiredness
- Drugs
- Alcohol
Give two factors which may affect braking diatance
- Adverse (wet/icy) road conditions
- Poor tyre/brake 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 theough the brake discs
To stop a car in a given distance , if its velocity is increased , what must happen to the braking force applied?
The breaking force must also be increased
State two consequences of a vehicle undergoing very large declarations
- Kinetic energy converted to heat is very high causing brakes to overheat
- Loss of control of the vehicle
