Unit 2 Section 1 Mechanics Flashcards
What is the difference between a scalar and a vector?
A vector has magnitude and direction while a scalar only has the former.
Is force scalar or vector?
Vector.
What are the 3 rules for bearings?
Start from north.
Go clockwise.
Have 3 figures.
What is free fall?
The motion of an abject going at an acceleration of g.
The weight is the only force acting on it.
What is a projectile?
Any object give an initial velocity and then left to move freely under the influence of gravity.
What does a curve on a velocity time graph mean?
The acceleration is changing.
What is inertia?
The resistance an object has to a change to its state of motion, including direction and speed.
What affects inertia?
The larger the mass, the greater the inertia.
What is weight?
It is the force experienced by a mass due to the gravitational field strength.
What is weight measured in?
Newtons.
How is weight found?
Mass X gravitational field strength.
What is the density equation?
Mass = density X volume.
Define centre of gravity.
The single point that the whole weight of the object can be considered to act through.
What is the critical angle of an object?
It is when the centre of mass is on the edge of the base area. The object will be balancing on its edge.
What do free body force diagrams show?
All the forces the world puts on an object, but not the forces the object puts on the world.
What is resolving a force?
Splitting up a force into different forces so the calculations are easier to work with.
What is a moment?
The turning affect of a force.
What is the principle of moments?
For a body to be in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point.
What is a couple?
A pair of forces of equal size which act parallel to each other but in opposite directions.
They don’t produce any resultant linear force but do produce a turning force (or torque)
What is the formula for finding a torque in a couple?
Torque(Nm) = size of one of the forces(N) X perpendicular distance between the forces (M)
What is Newton’s first law?
The velocity if a object wouldn’t change unless a resultant force acts on it.
What is Newton’s third law?
For every action there is an equal and opposite reaction.
If object A exerts a force on object B, then object B exerts an equal but opposite force on object A.
A book is put on a table. Explain the forces using newton’s laws.
It is not the third law as gravity pulls down on the books and the table pushes up on the books. These are 2 different sets of forces meaning it isn’t an example of the third law.
The forces are equal and opposite meaning nothing moves so it shows the first law.
What are the 2 types of friction?
Contact friction. Between solid surfaces.
Fluid friction.(drag or air resistance)
What affects the force of fluid resistance or drag?
The viscosity of the fluid.
It increases as speed increases.(normally directly proportional)
The shape of the object. The larger the area, the greater the resistance.
In which direction do frictional forces always act?
The opposite direction to the motion of the object.
They never cause things to move on their own.
They convert kinetic energy to heat.
What does terminal velocity look like on an acceleration time graph?
The acceleration falls to zero.
Define work?
The amount of energy transferred from one form to another when a force causes a movment.
What is the equation for work?
Work (J)= force(N)X distance(M)
Define 1 joule.
One joule is the work done when a force of 1 newton moves an object through a distance of 1 metre.
What are the equations to find power?
Power (W) = work done(J)
Time(s)
Power= force X velocity
What is the centre of mass?
The point at which all of the mass of an object appears to be.
When is an object stable?
It is stable when the action of the weight acts though the base.
A 650 kg car goes from 100 m/s to rest in 4 seconds. Find the magnitude of the braking force in newtons.
Find it in terms of G.
Acceleration =-25 m/s
650 X 25 = 16250 newtons of force.
16250 ÷ 650 ÷ 9.81 = 2.55 G
When is something in equilibrium ?
Sum of clockwise moments = sum of anticlockwise moments.
What is mechanical power?
The rate at which energy is transfered.
Define a moment.
The moment of a force about a point is equal to the force multiplied by the perpendicular distance between the line of action and the pivot.
Define velocity
The rate of change of displacement.
Define speed.
The rate of change of distance.
Define acceleration.
The rate of change of velocity.
How is acceleration found in terms of g?
Divide by 9.81
How is power found?
Force X velocity.
Work ÷ time
