Darkhan Kyzaibayev

Yernar Beketov

WORK - KINETIC ENERGY PRINCIPLE

WORK-ENERGY PRINCIPLE

The change in the kinetic energy of an object is equal to

the net work done on the object.

• This fact is referred to as the Work-Energy Principle and is often a very useful tool in mechanics problem solving. It is derivable from conservation of energy and the application of the relationships for work and energy, so it is not independent of the conservation laws. It is in fact a specific application of conservation of energy. However, there are so many mechanical problems which are solved efficiently by applying this principle that it merits separate attention as a working principle.

• For a straight-line collision, the net work done is equal to the average force of impact times the distance traveled during the impact.Average impact force x distance traveled = change in kinetic energy

• If a moving object is stopped by a collision, extending the stopping distance will reduce the average impact force.

WE STUDIED ABOUT WORK-ENERGY PRINCIPLES IN THE CLASS IN 8TH WEEK. GIVEN THAT, KNOWING THESE

PRINCIPLES ARE VERY IMPORTANT FOR EVERYONE, THE LECTURE ABOUT WORK-ENERGY PRINCIPLES WAS VERY

COMPELLING FOR US. PARTICULARLY, WE WERE INTERESTED IN THE USAGE OF WORK – KINETIC ENERGY PRINCIPLE IN EVERYDAY LIFE. THEREFORE, WE CAME UP

WITH THE IDEA TO STUDY ABOUT THIS PRINCIPLE FURTHER IN DETAILS ; CONSEQUENTLY, DESIRE TO KNOW MORE

ABOUT THIS PRINCIPLE INSPIRED US TO MAKE THIS PROJECT.

NON-STRETCHING SEATBELT

The task of the seatbelt is to stop you with the car so that your stopping distance is probably 4 or 5 times greater than if you had no seatbelt. A crash which stops the car and driver must take away all its kinetic energy, and the work and energy principle then dictates that a longer stopping distance decreases the impact force. For the car crash scene the stopping distance is one foot, the force on a 160 lb. driver is about 4800 lb. or 2.4 tons, and the deceleration about 30 g's. A moderate amount of stretch in the seatbelts will reduce the average impact force.

STRETCHING SEATBELT

A moderate amount of stretch in a seatbelt harness can extend the stopping distance and reduce the average impact force on the driver compared to a non-stretching harness. If the belt stretched 0.5 ft. in the example car crash scene, it would reduce the deceleration to 20 g's and the average impact force to 3200 lb. compared to 30 g's and 4800 lb. for a non-stretching seatbelt. Either a stretching or non-stretching seat belt reduces the impact force compared to no seatbelt.

NO SEATBELT!• With no seatbelt to stop the driver with the car,

the driver flies free until stopped suddenly

by impact on the steering column, windshield, etc.

The stopping distance is estimated to be about one

• fifth of that with a seatbelt, causing the average impact

force to be about five times as great. The work done

to stop the driver is equal to the average impact force

on the driver times the distance traveled in stopping.

A crash which stops the car and driver must take away

all its kinetic energy, and the work-energy principle then

dictates that a shorter stopping distance increases the impact force.

NEW INSIGHT• The work and energy principles are crucial in our daily live. Most

people don’t even realize how these principles are related to each other. This relation is well illustrated in the example of the usage of the seatbelt. The seatbelt is very useful in the way of saving our lives. It stops a person while a crash stops a car’s kinetic energy then work and energy principle occurs. Therefore, the person who doesn’t use a seatbelt puts in danger not only his/her lives but other passengers’ lives respectively. This is a great lesson for everyone to take more responsibility and to study physics.