Instructor’s Copy

Lab Worksheet: Drip, Drop

Background:

If air resistance is small, the rate at which a body falls in constant, regardless of its mass. The rate at which a body falls is determined by the gravitational force exerted on the body. On the surface of the Earth, acceleration due to gravity is close to 9.8 m/sec2. In this investigation you will determine acceleration due to gravity using two different methods.

Purpose: to be able to calculate acceleration due to gravity near the surface of the Earth

Materials:

String or wire about 1.5 m long pie plate

Hooked weight, 500 g meter stick

Timer beaker

Buret ring stand with buret clamp

Procedure – Part A: Measuring Acceleration Due to Gravity Using a Pendulum

A. Place the ring stand on a table so that the clamp

hangs over the side of the table. See Figure 1.

Tie one end of the string to the clamp. Attach the

50-g weight to the other end of the string.

B. Pull the weight back about ten degrees from its rest

position. Release the weight and record in

Data Table 1 the time (T) in seconds it takes to make

20 complete swings. One complete swing

is back and forth.

C. Measure the length (L) of the wire or string from the center of the weight to the ring stand.

Record this length to the nearest 001 m in the Data Table.

Data Table 1 Answers are approximate

Length (L) (m) / Time (T)
20 swings (sec)
1.5 m / 50 sec

Part B: Measuring the Acceleration of a Water Drop

D. Attach the buret to the ring stand with the buret

clamp (See Figure 2). Fill the buret about three

fourths full of water.

E. Place the pie pan on the floor beneath the buret. The pie

pan should be at least 1 m below the base of the buret.

F. Adjust the drip rate so that one drop just leaves the buret

when the previous drop hits the pie pan.

Watch the drop at the buret and listen for the sound.

G. After adjusting the drip rate, record in Data Table 2 the number of seconds it takes for 100

drops to hit the pie plate. Keep the level of the water in the buret approximately constant by

refilling it with a beaker.

Distance (d) (m) / Time (T)
100 drops (sec)
1.0 m / 46 sec

H. Measure the distance (d) from the tip of the buret to the pie plate. Record this distance to the

nearest 0.01 m in Data Table 2.

Observations: Part A

1. Calculate the time (T) for a single swing. (Divide the time for 20 swings by 20.)

50 sec = 2.5 sec

20

2. Calculate the acceleration due to gravity in m/sec2 using the formula:

AG = 39.5 . L

T2

Where AG = acceleration of gravity, L = length in meters, and T = times in seconds for one

swing.

AG = (39.5 x 1.5 m) = 0.5 m/sec2

(2.5 sec)2

Part B:

3. Calculate the time (T) for a single water drop to fall. (Divide the time for 100 drops by 100.)

46 sec = 0.46 sec

100

4. Calculate the acceleration due to gravity using the formula: AG = 2D

T2

Where AG = acceleration of gravity, D = distance in meters, and T = time in seconds for one

drop.

AG – 2(1.0 m)__ = 9.5 m/sec2

(0.46 sec)2

Analysis and Conclusions:

1. The acceleration of gravity is approximately 9.8 m/sec2. Which method was more accurate?

2. Can you offer possible reasons for your answer to question 1?

Answers will vary, but should reflect potential inaccuracies in measurement during either

Part A or Part B.

Critical Thinking and Application:

1. Compare the motion of the object in Part A with the motion of the water droplets in Part B. How

did the force of gravity influence each one?

The object in Part A moved in an arc, falling down and then swinging back up. It was the

force of gravity that pulled the object down to the low point of its arc each time. The water

droplets fell to the ground in a straight line. It was the force of gravity that caused them to

fall.

2. Study the formula used to calculate acceleration due to gravity in Part A. Assuming that AG in

constant, what must be true about the relationship between the length of the string and the time it

takes for the pendulum to make one complete swing?

The square of the time increases as the length of the string increases.

3. Suppose you performed Part A using strings of varying lengths. How would you expect your

calculated value of AG to compare with the results you obtained in this investigation?

Should be the same

4. Study the formula you used to calculate acceleration due to gravity in Part B. How is the time

taken for one droplet to fall related to the distance it falls?

The square of the time increases as the distance increases.