P8.1 - physics on the move 🚗 Flashcards
How would you measure … the of a 100m sprinter?
- speed
- distance
- time
Speed - electronic timing system
Distance - measuring tape/trundle wheel
Time - pressure sensor to start? Laser beam to end
How would you measure … the of a car on a road
- speed
- distance
- time
Speed - speed gun
Distance - measuring tape/trundle wheel
Time - time between two photos
How would you measure … the of a cyclist?
- speed
- distance
- time
Speed - wheel sensor
Distance - wheel diameter
Time - magnetic sensor that detects one rotation (how quickly one rotation happened)
Typical speed of a person walking (m/s), then convert it to mph
1 m/s, 2.2mph
Typical speed of a person running (m/s), then convert it to mph
5m/s, 11mph
Typical speed of a person cycling (m/s), then convert it to mph
7m/s, 15mph
Typical speed of a person Olympic cycling (m/s), then convert it to mph
20m/s, 45mph
Speed of Strong wing (m/s), then convert it to mph
13m/s, 30mph
Average speed of car (m/s), then convert it to mph
22m/s, 50mph
Typical speed of train (m/s), then convert it to mph
56m/s, 125mph
What is reaction time? (And give an example of timing a runner)
The lag between you seeing something, and your action as a result
ie. when runner finishes finishing line light reflects from runner, hits your retina, impulse travels to brain, back down to finger, then presses stop button on stopwatch
What is a human’s average reaction time?
0.2 seconds
How do you measure reaction time + improve it?
Catch a falling ruler, play video games
What is thinking distance? (In a car)
Distance that a car travels while the driver reacts to a hazard (so before they react, ie. pressing brakes)
What factors affect thinking distance (and why)?
- alcohol consumption
- using drugs/ medicines
- being tired
AFFECTS reaction time of individual - distraction by other ppl in the car
- eating/drinking
- using radio/ Satnav
AFFECTS as they are distracted, so not on full alert
How would being under the influence of drugs/alcohol make you more likely to be in a car crash?
Since your reaction time greatly increases, perhaps double or triple that of it would normally be.
That means you could travel almost double or triple the distance before even braking
What is braking distance?
The distance that a car travels while the driver is braking
ie. after the driver applied the brakes
What factors affect braking distance? (4)
- quality of brakes (ie. are they worn out, can they apply pressure effectively)
- surface that the car is driving on (ie. if ice then less friction = larger braking distance)
- speed of the car while travelling
- mass of car/ passengers within
larger mass = larger kinetic energy = more energy to be converted to stop = larger braking distance
What is stopping distance?
The total distance that the car travels from the moment the driver sees the problem to until the car is stationary
Ie. Thinking distance + braking distance
What is the thinking distance and braking distance for 70mph?
Thinking distance = 21m
Braking distance = 75m
What is key about the relationship between speed and braking distance?
And what does that mean in terms of safety?
The higher the speed, the braking distance drastically increases (imagine the corona curve), so a much much larger distance is needed to stop a car travelling at 70mph (almost 100m)
Therefore, it’s very dangerous to travel at high speeds (could easily crash anywhere, and you have no control)
explain the dangers of a large deceleration
- a large force is exerted on the passengers and the vehicle
- seatbelt can cause compression injuries
- injure internal organs (ribs stopped by seatbelt, but organs are still moving)
what is the equation to find out the forces involved in typical situations on a public road?
(if you have mass + acceleration)
F = M x A
suggest what causes a ‘large deceleration’ on the road
braking hard
what in a car is designed to reduce the effects of the large deacceleration?
- seat belts
- crumple zones
- air bags
how does a seat belt reduce the injury effects of the large acceleration?
- slightly stretches under large forces
- which increases the distance the passengers move (reducing force experienced)
how does a crumple zone reduce the injury effects of the large acceleration?
- soft areas at front of car DEFORM (absorbs energy to compact)
- increases time taken for car to stop
REDUCE FORCE/ACCELERATION
how does an air bag reduce the injury effects of the large acceleration?
- prevents head from hitting steering wheel
- or jerking back (neck injuries)
- head hits bag = slows down = increase time = less force on neck
