How does a dropped object behave?
!Does the object accelerate, or is the speed constant?
!Do two objects behave differently if they have:
!different masses?
!different shapes?
Acceleration Due to
Gravity
" Earth exerts a gravitational force on objects
that is attractive (towards Earth’s surface).
" Near Earth’s surface, this force produces a constant acceleration downward.
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To measure this acceleration, we need to slow down the action.
Galileo was the first to accurately measure this acceleration due to gravity.
By rolling objects down an inclined plane, he slowed the motion enough to establish that the gravitational acceleration is uniform, or constant with time.
Inclined Plane
Experiment
!Does the marble pick up speed as it rolls?
!Is it moving faster at the bottom of the incline than it was halfway down?
" Flashes of a stroboscope
illuminate a falling ball at equal time intervals.
" Distance covered in successive time intervals increases regularly.
" Since distance covered in equal time intervals is increasing, the velocity must be increasing.
" Average velocity for a time
interval is given by dividing the distance traveled in that time interval by the time of the interval.
" For example, between the
2nd and 3rd flashes, the ball travels a distance of
4.8 cm - 1.2 cm = 3.6 cm in a time of 0.05 s:
3.6 cm v= = 72 cm/s
0.05 s
!
" The velocity values steadily
increase.
Time
0s
0.05 s
0.10 s
0.15 s
0.20 s
0.25 s
0.30 s
0.35 s
Position
0 cm
1.2 cm
4.8 cm
11.0 cm
19.7 cm
30.6 cm
44.0 cm
60.0 cm
