Mechanics Flashcards
What is a scalar quantity?
A quantity with only magnitude
Name 3 Scalar Quantities
Speed, magnitude and distance
What is a vector quantity?
A quantity with magnitude and direction
Name 6 Vector Quantities
Acceleration, Displacement, Velocity, Force and Weight
What are the SUVAT Equations
v = u +at, s = (v -u)t / 2, v^2 = u^2 + 2as, s = ut + 1/2at^2
What does the gradient mean on a displacement - time?
Velocity of an object
What does it mean when a displacement graph curves?
The object is uniformly accelerating
How do you find instantaneous velocity on a displacement - time graph?
Draw a tangent to the point of interest and find the gradient
What happens when the line is horizontal on a displacement - time graph?
The object is stationary
How do you find average velocity?
Average velocity = Total Displacement / Total Time
What does the gradient of a velocity time graph show?
The object is accelerating
What does area under the graph on a velocity - time graph mean?
The displacement of the object
What does it mean if the graph is curved on a velocity - time graph?
The graph has increasing or decreasing acceleration
What does it mean if the line is horizontal on a velocity - time graph?
Stationary or at a constant velocity
What does area under graph mean on a velocity - time graph?
Displacement of object
What does it mean if line is positive on an acceleration - time graph?
The object is accelerating
What does it mean if line is negative on an acceleration - time graph?
The object is decelerating
How do you calculate the horizontal velocity?
Cos(Angle)
How do you calculate the vertical velocity?
Sin(Angle)
Projectiles Key Facts
Horizontal velocity is a constant and acceleration is 0, and vertical velocity changes due to acceleration -9.81, apex vertical velocity is 0 and time to go up equals time to go down.
Distance Equation
Distance = Speed x Time
Displacement Equation
Displacement = Velocity x Time
Acceleration Equation
Acceleration = Change in Velocity/ Change in Time
Weight Equation
Weight = Mass x GFS
What is terminal velocity?
An object travelling through a medium will reach maximum speed when air resistance equals the driving force.
How do you increase drag on an object?
Increase speed, increase air resistance, increase surface area and make it less stream line
What is momentum?
Momentum is the product of an objects mass and velocity.
Momentum equation
Momentum = Mass x Velocity
What is momentum measured in?
Momentum is a vector quantity measured in Ns
What is the law of conservation of momentum?
The sum of momentum before the collision is equal to the sum of momentum after the collision in a closed system in any direction.
Momentum Formula when objects collide and separate
MaUa + MbUb = MaVa + MbVb
Momentum formula when objects collide and stay together
MaUa + MbUb = V(Ma + Mb)
What happens in elastic collision?
Total energy and total kinetic energy is conserved.
What happens in inelastic collision?
Total energy is conserved and total kinetic energy is not conserved.
What is impulse?
The impulse of a force is equal to the change in momentum of a mass when subjected to a resultant force.
Impulse equation
Resultant Force = Change in momentum / Time Interval
What is a resultant force?
The sum of all the forces acting on an object when the sum is not zero
What is friction?
The resistance to motion due to contact forces
What is drag?
A frictional force caused by collisions between the travelling object and particles in a medium e.g. air resistance
What factors affect drag?
Surface area , speed and shape
What is Newtons 1st Law?
An object will stay stationary or at a constant velocity if there is no resultant force applied
What is Newton’s 2nd Law?
When a resultant force acts on a body the rate of change of the bodies momentum is equal to that force (F = m x a)
What is Newtons 3rd Law?
When body A exerts a force on body B, body B exerts an equal in magnitude but opposite in direction force ( of the same type) on body A.
What is a moment?
The moment of a force is its turning effect about a fixed point/pivot
What is the moments equation and measurements?
Moment (Nm) = Force (N) x Perpendicular distance from force to pivot (m)
What are the units for a moment?
Newton metres (Nm)
What is the principle of moments?
Total moments acting clockwise equal the total moments acting anticlockwise when in equilibrium
What is a couple?
A couple is a pair of equal and opposite forces
What is the moment of a couple called?
A torque
The equation to calculate a torque?
Torque (Nm) = Force (N) x Perpendicular distance between couple (m)
What is the centre of mass of an object?
The point through which an objects weight appears to act (average position of mass)
How would you increase an objects stability?
You would lower the centre of gravity and widen the base
What is work done?
Work is done when a resultant force acts on an object causing the object to move a certain distance in the direction of the force.
What is the work done equation?
Work Done (J) = Force (N) x Distance (m)
What is work done measured in ?
Work done is measured in Joules (kgm^2s^-2) and is a scalar quantity
What is energy?
Energy is the ability of an object to do work
What is the principle conservation of energy?
Energy cannot be created or destroyed only transferred between stores
What is the kinetic energy equation?
1/2 x mass x velocity^2
What is the gravitational potential energy equation?
mass x gravitational potential x change in height
What is the elastic potential energy equation?
1/2 x spring constant x extension^2 or 1/2 x force x extension
What is power?
Power is the rate of energy transfer
What is the power equation?
Power (W) = Energy transfer or Work done (J) / Time (s)
What is the efficiency equation?
Efficiency = Useful Output / Total Input
