Transcript Lang Gar Part 2 - 2011-3S1

Done by: Liu Du Kai Ying
Dexter Kuah
Nicholas Lim
Momentum
Given by the formula:
p = mass x velocity
Force of Impact
The force of impact on the driver when a car crash occurs is
given by the formula:
Momentum
Time
=
Mass X
Velocity
Time
As you can see, the change in momentum in this case is
changed with the change in acceleration
However, we are unable to change the mass of the car or the
velocity at which it travels
Thus, we can only extend the impact time to reduce the force
via a few safety precautions in the car
Seatbelt
This is the most common item in all cars
Protects the passenger from harm by reducing inertia
Based on Newton’s 1 st law:
 An object will remain in a state of rest or continue
traveling at constant velocity, unless acted on by
another force
The seatbelt can thus help to be this resistive force
Seatbelt
The use of the seatbelt can be explained using Newton’s
3rd law:
 If object A exerts a force on object B, object B will exert an equal
force on object A
Thus, the seatbelt in the case when the passenger is thrown
forward, will exert an equal force back on the passenger, thus
reducing the force acting on him
Seatbelt
Why the seatbelt works, is based on physics equation on
impulse:
In the case of a seatbelt, it extends the time of the
collision, and thus reduces the average impact force
Example
A car is travelling at a speed of 100km/h
The passengers inside are all travelling at a speed of
100km/h
In the event of an accident, the car stops very fast,
slowing down
However, the passengers inside are still moving at
100km/h
Thus, the seatbelt exerts a force back on the passenger,
thus causing him to slow down and extending the time of
collision, preventing more severe injuries
Air bags
Air bags inflate when the car decelerates extremely
quickly
This surrounds the passenger like a cushion
Although the use of seat belts can allow the passenger’s
body from flying, the passenger’s head will still
experience a whiplash
The body stays, but the head is thrown forward
Air bags
Based on Newton’s 3 rd law, the air bag will serve as the
opposite force to prevent the passenger’s head from
flying further in front
Based on Newton’s 1 st law of inertia, an object will
continue in its state of motion unless acted on by another
force
 The airbag can thus serve as the resistive force to prevent
the head from slamming into the windscreen with a great
force since the time of collision is extended
Car Brakes
One of the most important items in a car are the ones
which slow down the car’s velocity
The car brakes help by increasing energy in the opposite
direction, thus slowing the car’s velocity
There are a few aspects of physics in a car brake
 1) The brake pedal
 2) The car brake itself
Car Brakes
The pedal uses a lever system as our legs are not strong
enough to slow down the car
One side of the lever in the pedal is twice as long as
the other
 As our foot provides a small force to the longer side of
the pedal the lever system allows the force to be
multiplied because the force before must be equal to the
force after
This allows the car to slow down with enough energy
Car Brakes
The car brakes itself uses hydraulic pressure and friction
to slow down the velocity of the car
When the pedal is stepped down, the friction between
the car tires and the surface of the road increases
The amount of force acting in the opposite direction
increases
Thus, the resultant force decreases
Car tires
The car tires have patterns and markings on them so as
to increase friction between the road surface and the car
This increases friction working in the opposite direction,
and thus sl0wing the car down
Crumple zone
The crumple zone AKA crash zone is the part of the car
that will collapse upon impact
Upon this collapse, the crumple zone absorbs the force
of the impact, reducing the amount of force acting on the
passenger
Crumple zone
This can be explained also with the equation of impulse
During an accident, the crumple zone extends the time
of the collision
This thus reduces the force acting on the passengers
References
 http://www.scienceclarified.com/everyday/Real-Life-Chemistry-Vol-3Physics-Vol-1/Momentum-Real-life-applications.html
 http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html
 http://www.physicsclassroom.com/class/momentum/u4l1c.cfm
 http://www.youtube.com/watch?v=i_S9qV8vLwI
 http://cnx.org/content/m31492/latest/
 http://www.grc.nasa.gov/WWW/K-12/airplane/newton2.html
 http://docs.google.com/View?id=dcv8dft6_904dxf9jxvt
 http://www.money-zine.com/Financial-Planning/Leasing-or-Buying-aCar/Car-Safety-Features/