Mechanics Flashcards
What are the vector quantities?
Displacement, velocity, acceleration, force, momentum
How do you calculate displacement from a velocity time graph?
Calculate the area under the graph
How do you calculate displacement from a velocity time graph if it is curved?
Use the count the squares method
What is the definition of stopping distance?
Total distance travelled from when the driver first sees the reason to stop to when the vehicle stops.
What is the equation for stopping distance?
Stopping distance = thinking distance + braking distance
What is the definition of thinking distance?
Distance travelled between moment when you first sees a reason to stop, to the moment when you use the brake.
What is the definition of braking distance?
The distance travelled from the time the brake is applied until the vehicle stops.
What factors affect stopping distance?
Speed of vehicle, condition of brakes, condition of tires, condition of the road, weather conditions, alertness to the driver.
What is the equation for thinking distance?
Thinking distance = speed x reaction time
How would you calculate braking distance?
Use SUVAT equations
How would you draw a scale drawing?
Decide on a scale for the length of vectors and use a protractor to draw angles accurately. Measure the length of the unknown vector and convert to Newtons using the scale.
What is the definition of drag?
A frictional force that resists the motion of an object through a fluid.
Define a Newton
The force that causes a mass of
one kilogram to have an acceleration of one metre per second squared.
When and why is F=ma no longer valid?
Due to Einstein’s Theory of Special Relativity, mass increases if the object is travelling very close to the speed of light.
Define centre of mass of an object
The single point that you can consider its whole weight to act through.
Where is the centre of gravity for a regular shaped object?
Where its lines of symmetry meet.
Where does the centre of mass act for a uniform object?
At the centre of the object.
Define a moment
Moment = force x perpendicular distance to the line of action of the force from the axis or point of rotation
Define the principle of moments
For a body in equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments about that same point.
Define a couple
A pair of forces equal in size acting parallel to each other but in opposite directions.
What features must a couple have?
Forces must be equal in magnitude
Forces must be parallel but opposite in direction
Forces must be separated by a distance d
Define torque of a couple
Torque of a couple = size of one of the forces x perpendicular distance between the forces
Define work done
Work done = force x displacement in the direction of the force
Define a Joule
1 Joule is equal to the work done by a 1 Newton force moving an object through 1 metre.
Define the principle of conservation of energy
Energy cannot be created or destroyed, it transfers between different forms.
Define power
Rate of energy transfer
Define a Watt
Work done of 1 Joule in 1 second
Why is no mechanical device 100% efficient?
There is always a waste heat due to work done against resistive forces such as friction.
Define pressure
Normal force per unit cross sectional area
Define Pascal
1 Newton per metre squared
What do the letters represent in the equation p= ρgh?
p - pressure at the base of the column
ρ - density of the fluid
h - height on the column
State archimedes principle
For an object fully or partly submerged in a fluid, there is a force of upthrust equal to the weight of the fluid displaced.
What happens to wood released from the bottom of a tank full of water?
It will eventually float, as the wood speeds up the drag will increase, it may reach terminal velocity if
W + D = U before the surface.
Write an equation for the forces acting on wood when it floats
W = U
Why does a mass still have some kinetic energy at max height?
It has a horizontal component of KE
What does the magnitude of drag depend on?
Cross sectional area of the moving object
Viscosity of fluid
Velocity of object
Roughness of surface of the object
