Chapter 3.1 - Motion Flashcards
Instantaneous Speed
The speed at a certain time
Displacement
A vector quantity that represents how far an object has travelled from its starting point in a given direction
Average Speed
Distance / Time
Average Velocity
Displacement / Time
Distance
A scalar quantity that shows how far something travelled along a certain route
Velocity
A vector quantity that shows rate of change of displacement
Acceleration
A vector quantity, the rate of change of velocity
Gradient of displacement-time graph
Velocity
Gradient of velocity-time graph
Acceleration
Area under velocity-time graph
Displacement
The 4 SUVAT equations
v = u + at s = 0.5(u + v)t s = ut + 0.5at^2 v^2 = u^2 + 2as (s = vt - 0.5at^2)
value of g
9.81
Acceleration of a body in free fall
-g
Is horizontal velocity independent of vertical
yes
The two types of approaches for measuring g
Direct e.g. timing a falling ball
Indirect e.g. timing a pendulum
Describe the experiment to measure g (trapdoor)
- Set up a steel ball supported by an electromagnet
- Turn of current so ball is released and clock started
- When ball hits trap door a connection is broken and timer is stopped
- We now have u, s, t and want to find a so we can rearrange a SUVAT
- Can plot a graph with different values of s (and t)
Potential sources of error for g trapdoor experiment (3)
- Electromagnet current too high can cause delay
- If distance is too large air resistance might have a noticeable effect
- Measurement of distance
Experiment to measure g (light gates)
- A piece of card is dropped from a certain height above a light gate
- Light gate and data logger calculate v, u = 0, s = measured so a can be calculated
- A graph of v^2 against s can be plotted with the gradient being 2g
Assumptions made by light gate g experiment
The cards velocity is constant as it travels through the gate
Thinking distance
Distance a car travels between driver seeing hazard and applying brakes
Braking Distance
Distance between applying brakes and coming to rest
Stopping distance
thinking distance + braking distance
Factors that increase thinking distance (5)
- high speed
- tiredness
- alcohol / drugs
- Distractions
- Age
Factors that increase braking distance (5)
- high speed
- poor road conditions
- poor brake conditions
- poor tyre conditions
- mass of car
Equation for thinking distance
reaction time * speed
Relationship between braking distance and speed
squared
Why is braking distance proportional to speed squared
Because brakes constantly do work against the car, and the total energy is 0.5mv^2
Equipment used to investigate motion and collisions of objects
- Trolleys, light gates, data loggers
- Video recording and analysing frame by frame
