Forces and motion Flashcards
Acceleration eq
a = Δv/t Acceleration is negative acceleration (-)
What is Weight
The force acting on an object due to gravitational attraction
What is friction
The force which opposes the motion of an object Always in opposite direction to motion
Momentum eq
p = m x v
vector kg m/s
What is stopping distance
The total distance travelled during the time it takes for a car to stop in response to some emergency
It can be written as an equation involving two distances:
Stopping distance = Thinking distance + Braking distance
Principle of Moments
When an object is balanced, the total anticlockwise moment about a pivot = total clockwise moment about a pivot
Therefore you can use F 1 d 1 = F 2 d 2 If not it will turn
What happens when maverick opens his parachute?
There is a larger S.A so there is now more air resistance Reduces T.V
What is Terminal Velocity
The maximum speed that a moving object is able to reach Friction increases with speed ONLY till a certain point
Factors affecting breaking distance
How fast you are going, faster u r going, further distance
Mass of vehicles, larger mass, larger distance Quality of breaks Road surface/weather
What is the limit of proportionality (elastic limit)
When objects return to their original shape when the stretching force is removed
What is a moment
The turning effect of a force about a pivot
How to find COG
Suspend the shape and use a Plumb line from the same point Draw a line along it Do the same thing from different points COG is the centre of where lines point
When does the momentum of an object change
If it changes direction Its mass changes Accelerates or deccelerates
Resultant force eq
F = m x a
3 types of friction
Between solids - gripping Between solids sliding past each other Resistance/drag from fluids, e.g water or air
Speed, Velocity, Acceleration
Speed = D/t S = vt acceleration = (v-u)/at change in velocity/time v 2 =u 2 +2as
What is acceleration
Rate of change of velocity (m/s 2 )
Centre of Gravity
The point through which weight of a body acts A freely suspended object will swing until its COG is vertically below the point of suspension. You can calculate this with lines of Symmetry
Supporting a beam
A light beam has no mass, therefore forces must be upwards (See book)
Example of moment
the door handle is placed on the opposite side to the hinge
This means for a given force, the perpendicular distance from the pivot (the hinge) is larger
This creates a larger moment (turning effect) to make it easier to open the door
Opening a door with a handle close to the pivot would be much harder, and would require a lot more forceDoor handle is placed opposite to the hinge This means for x force the perpendicular distance from the hinge (pivot) is larger Therefore larger moment - Easier to open IF handle was near pivot it would be harder
How do u calculate moment
M = F x d (Nm) d= perpendicular distance
What are the safety measures in a vehicle
Crumple zone- Crumples increasing time to impact Seat belts - stretch increasing time taken Air bags - slow you down All of this reduces the force as time increases F = ([change] in momentum)/t
Newtons 3rd law
Whenever two bodies interact the forces they exert on each other are equal and opposite When 2 objects collide (momentum) one will generally accelerate and one will deccelerate
Newtons 2nd law
A resultant force means acceleration (f=ma)
What is Newtons 1st law
As long as an object has 0 resultant force it was stay still or travel at a constant velocity (forces r balanced)
Force and Change in Momentum Eq
F = (mv-mu)/t Force - change in momentum / time
Can be positive and negative
Law of conservation of momentum
Momentum before = Momentum After
What is inelastic deformation
When objects remain stretched and do not return completely to their original shape even when the stretching force is removed
Examples of materials that undergo inelastic deformation are:
Plastic
Clay
Glass
What is Elastic Deformation
When objects return to their original shape when F is removed e.g. Rubber bands, Fabrics, Steel Springs
What is Hooke’s law?
The extension of an elastic objec t is directly proportiona l to the force applied up to the limit of proportionality (elastic limit)
Explain T.V in a skydiver [Maverick ejecting from F-14]
When he falls he has initially accelerates due to his weight, air resistance increases (upwards F) until it balances weight. As he speeds up, air resistance increases, now resultant F = 0 Therefore a = 0 and Terminal Velocity
Factors affecting thinking distance
How fast driver is going Reaction time (drugs, alcohol, old age, tiredness)
What is stopping distance made out of
Thinking Distance + Distance travelled in the time taken to react (m) Braking distance - Distance travelled once break has been pressed (m)
Weight formula
W = m x g
What is Weight
The force acting on an object due to gravitational attraction
What is a vector quantity
Has magnitude and direction e.g. weight
What is a scalar quantity
Only has magnitude e.g. mass
What is a reaction force
The force between twow objects in contact Acts perpendicular to surface & away from it
What is a force
Forces cause changes in: -Speed -Direction -Shape
