Chapter 2.8 Gravity Safety Features in Vehicles1. Crumble Zone

The crumple zone increases the reaction time of collision during an accident.This causes the impulsive force to be reduced and hence reduces the risk of injuries.

2. Seat Belt

Prevent the driver and passengers from being flung forward or thrown out of the car during an emergency break.

3. Airbag

The inflated airbag during an accident acts as a cushion to lessen the impact when the driver flings forward hitting the steering wheel or dashboard.

4. Head Rest

Reduce neck injury when driver and passengers are thrown backwards when the car is banged from backward.

5. Windscreen

Shatter-proof glass is used so that it will not break into small pieces when broken. This may reduce injuries caused by scattered glass.

6. Padded Dashboard

Cover with soft material. This may increases the reaction time and hence reduce the impulsive force when passenger knocking on it in accident.

7. Collapsible Steering Columns

The steering will swing away from drivers chest during collision. This may reduce the impulsive force acting on the driver.

8. Anti-lock Braking System (ABS)

Prevent the wheels from locking when brake applied suddenly by adjusting the pressure of the brake fluid. This can prevents the car from skidding.

9. Bumper

Made of elastic material so that it can increases the reaction time and hence reduces the impulsive force caused by collision.

10. Passenger Safety Cell

The body of the car is made from strong, rigid stell cage.This may prevent the car from collapsing on the passengers during a car crash.

Gravitational Field

A gravitational field as a region in which an object experiences a force due to gravitational attraction.

Gravitational Field Strength1. The gravitational field strength at a point in the gravitational field is the gravitational force acting on a mass of 1 kg placed at that point.2. The unit of gravitational field strength is N/kg.

3. The gravitational field strength is denoted by the symbol F=Force acted on an objectm = mass of the object.g = gravitational field strength

Gravitational Acceleration1. The gravitational acceleration is the acceleration of an object due to the pull of the gravitational force.2. The unit of gravitational acceleration is ms-23. Gravitational acceleration is also denoted by the symbol "g".

note: Gravitational Field Strength vs. Gravitational Acceleration1. Both the gravitational field strength and gravitational acceleration have the symbol, g and the same value (10ms-2) on the surface of the earth.2. When considering a body falling freely, the g is the gravitational acceleration.3. When considering objects at rest, g is the Earths gravitational field strength acting on it.

Weight1. The weight of an object is defined as the gravitational force acting on the object.2. The SI unit of weight is Newton (N)

WeightMass

Depends on the gravitational field strengthIndependent from the gravitational field strength

Vector quantityScalar Quantity

Unit Newton (N)Unit: Kilogram (kg)

Free Falling1. Free falling is a motion under force of gravity as the only force acting on the moving object.2. Practically, free falling can only take place in vacuum.

Free Falling 1 - Falling from High PlaceWhen an object is released from a high place,1. its initial velocity, u = 0.2. its acceleration is equal to the gravitational acceleration, g, which taken to be 10ms-2in SPM.3. the displacement is the of the object when it reaches the ground is equal to the initial height of the object, h.

Case of Free Falling 2 - Launching Object UpwardIf an object is launched up vertically,1. the acceleration = -g (-10ms-2)2. the velocity become zero when the object reaches the highest point.3. the displacement of the object at highest point is equal to the vertical height of object, h4. the time taken for the object to move to the maximum height = the time taken for the object to fall from the maximum point to its initial position.

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