Motion and Forces Flashcards
What is a vector?
A quantity with a magnitude and a direction e.g. Force, lift, thrust, velocity, displacement
What is a scalar?
A quantity with only a magnitude e.g. Length, mass, area, volume, speed, work
What us displacement?
The straight line distance from start to finish
What is velocity?
Speed in a direction
What is the equation for velocity?
Displacement / time
What does the gradient represent on a distance-time graph?
Speed. When it is flat, speed is 0. It can be calculated by change in y / change in x or with a tangent.
What is the equation for speed?
Speed = distance / time
What does the area under the line represent on a velocity-time graph?
Distance travelled
What is the equation for final velocity?
Final velocity^2 - Initial velocity^2 =2accelerationdisplacement
V^2 - u^2 = 2as
What is mass (m)?
The amount of matter in something
Measured in kg
Does not change
What is weight (W)?
The force acting on a mass due to gravity
Measured in N
Changes when gravity changes
What is gravity (g)?
An acceleration due to gravitational attraction of a force
Measured in m/s^2 or N/kg
Depends on size of the big mass and distance from it
Has a value of 10m/s^2 on Earth
What are the equations for force and weight?
Force = mass * acceleration F = ma Weight = mass * gravity W = mg
What are Newton’s three laws?
- An object will not move or move at a constant velocity unless acted on by an external force
- F = ma
- Every action has an equal and opposite reaction
What is circular motion?
When an object is moving in a circle it is travelling at 90 degrees to the force of tension. Its velocity is 90 degrees to it. Centripetal force is in the same direction to tension, pulling it in. For circular motion to occur there must be a centripetal force at 90 degrees to the tangential velocity.
What is centripetal force?
The force towards the centre in a circular motion
What is conservation of motion?
In a closed system momentum must be conserved. This means that the total momentum before is the same as the total momentum after an event. As p1 = p2, mv1 = mv2, so you can work out resultant velocity or the second object’s mass if given enough information.
What is the formula for momentum?
Momentum = mass x velocity P = mv kgm/s = kg * m/s
What is the formula for work done?
Work done = force x distance in direction of force
W = Fd
J = N * m
What is power?
How quickly energy is transferred
What is the equation for power?
Power = energy transferred / time Watt = joules / seconds
What is the equation for kinetic energy?
Kinetic energy = 1/2 x mass x velocity^2
KE = 1/2mv^2
What is the equation for distance?
Distance = (1/2 x mass x velocity^2) / force (from the breaks) D = (1/2mv^2)/F
What is the equation for force with mass, velocity and time?
Force = (mass x change in velocity) / time F = (m*v-u)/t OR Force = Change in momentum / time F = (mv - mu)/t
What are some car safety features?
Airbags
Crumple zones
Seatbelt
How do car safety features work?
They increase the time in a collision, reducing the force.
What is an impulse?
Change in momentum, or force x time. Its units are Ns or Mm
What is the equation for acceleration?
Acceleration = Change in velocity / time a = (v-u)/t
How can you investigate the motion of a trolley on a ramp?
Put a trolley with a card on onto a ramp. Put two light gates on the ramp, so that the trolley will disrupt them when passing. Adjust the height of the ramp until the trolley just begins to move. The light gates will record the speed and time, so acceleration can be worked out. Attach the trolley to a hanging mass by a string and repeat with different masses.
What is inertia?
The tendency for motion to remain unchanged. Unless acted on by a resultant force, an object will stay at rest or at a constant velocity. An object’s inertial mass measures how difficult it is to change the velocity of an object (m=F/a)
What is the equation for stopping distance?
Stopping distance = Thinking distance + Braking distance
What factors affect thinking distance?
Reaction time: includes tiredness, alcohol, drugs, and distractions
Speed
What factors affect braking distance?
Speed
Mass of the car
Condition of the breaks
Friction between tyres and road
How can you measure someone’s reaction time?
Use the ruler drop test:
Rest your arm on the edge of a table. Get someone to hold a ruler at the top of your hand and drop it. The further it fell, the longer the reaction time.
What is the average mass of a car, a single decker bus, and a loaded lorry?
Car: ~1000kg
Single decker bus: ~10,000kg
Loaded lorry: ~30,000kg
