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Suggested
Experiments
Explanation
of Newton's second law of motion
Tilt the runway at an angle such that a trolley will move down the runway
with uniform velocity when slightly pushed. In this way, the runway is
friction-compensated. Pull the trolley down the runway with an elastic
cord stretched to the same length as the trolley. (pic.1) Label the tape
as 1. Repeat with two cords in parallel. Label the tape as 2. Repeat with
two cords connected to two trolleys. Label the tape as 3.
pic.2 shows the three tapes obtained. One stretched cord connected to
one trolley causes the same acceleration as two stretched cords connected
to two trolleys. Two stretched cors connected to one trolley causes a
greater acceleration than one stretched cord connectd to one trolley.
To be quantitative, we may measure the acceleration for each tape by constructing
a tape chart. It is found that the acceleration for tape 2 is twice that
for tape 1 and tape 3. In this experiment all elastic cords are stretched
by the same amount. there force, two stretched cords set up twice the
elastic force as one stretched cord. In addition, the mass of two trolleys
is obviously twice that of one trolley.
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Explanation
of Newton's third law of motion
Push the toy car several times on the bench. Then place it on the cardboard
above a think layer of polystyrene beads as showan at the right hand side
The toy car moves forward due to an action exerted on the wheels by the
cardboard. The cardboard moves backwards due to a reaction exerted on
the cardboard by the wheels. The two forces act in opposite directions.
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