עמוד:35

When a car brakes , the brake pads ( or shoes ) rub against the disc ; friction is created between the tires and the road as well . In this state , the car’s kinetic energy turns into heat , in both the tire and the road . The law of conservation of energy applies , of course , in this case too : the total amount of heat created in the different places such as the brakes , the tires , and the road after the car stops is equal to the kinetic energy the car had before braking . And what happens to the kinetic energy of the pendulum swinging through the air ? Activity Experimentation The Motion of a Pendulum Objective : To examine the motion of a pendulum over time . Equipment : A pendulum composed of a piece of string , with a weight at the end . Experimental Procedure : Hold the end of the pendulum’s string and raise the ball to a certain height . Note this height . Release the ball , this time letting it continue until it stops . What happens to the pendulum’s kinetic energy ? Does this experiment contradict the law of conservation of energy ? When the pendulum finally comes to a stop , this does not contradict the law of conservation of energy . After the pendulum is released , it moves , and in its movement it encounters air resistance , or friction . This friction causes its kinetic energy to transform into heat . During the pendulum’s movement , more and more kinetic energy turns into heat , gradually diminishing the kinetic energy , until the pendulum finally comes to a stop , since all of its kinetic energy has turned to heat . The pendulum’s energy has not disappeared and its amount has not changed . It was merely converted from kinetic energy to heat . Questions 1 . What is the pendulum’s position when all of its energy has been converted to heat ? Explain . 2 . If you touch the pendulum before its release and then after it stops , you will not feel any difference in temperature . Try to hypothesize why .

מטח : המרכז לטכנולוגיה חינוכית


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