Newton's Second Law VTL - Ryerson Department of Physics

Newton’s Second Law
Objective
The purpose of this experiment is to show the relationship between force and
acceleration in a friction-free environment and to illustrate the concept of mass.
Apparatus
Air-cushioned track and glider
Weights and hanger
String
Pulley and clamps
Vernier Lab Pro
2 Vernier photogates
Fig. 1. Newton’s Second Law Apparatus
The glider is attached by a string to a hanger hanging at the end of a string passing
over a pulley clamped to the end of the air track. Transfer of masses from the cart
to the hanger will enable variation of the acceleration of the cart while keeping the
total mass of the system constant.
Software Configuration
Open the Vernier Logger Pro 3 application. Locate and open the file
NewtonSecondLawLab.cmbl.
Measure the length of the plate on top of your air-track cart. Within Logger Pro,
open the Data > User Parameters menu. Replace the default CartLength value
with your measured value.

Procedure
1. Set the two photogate timers over the track. Measure and record the distance
L between the photogates (make L about 60 cm). Make sure the cart does not
touch them as it passes underneath. Note, the distance L between the gates must
remain the same for all trials.
2. Attach a weight hanger to the glider by means of a string placed over the
pulley. The length of the string (approx. 130 cm) should ensure that the glider
clears the second photogate before the hanger touches the floor.
3. Put 40 g on the glider (balanced 20 g on each side).
4. Place the glider on the track at the starting position. Mark the starting position
with masking tape and a pencil mark, such that additional trials start from the
same place. Hold the glider and press the “Start Collection” button on the Logger
Pro screen. Release the glider.
5. After the glider has cleared the second photogate, the timers should read the
length of time t1 and t2 the glider took to pass under. Click Experiment > Store
Latest Run to store the data.
Repeat three times, releasing the cart from the same point and making sure the
photogates remain in the same position to ensure consistent values. Take average
values of v1 and v2.
[Note, it is recommended to save your data for each set of three trials of a
particular mass, e.g. Trials-Mass5g, Trials-Mass15g, etc. Save each file to the
Desktop of the computer. Once all trials have been completed, copy the files to a
USB key or e-mail to your account. All data is automatically deleted from the
computers at logoff.]
6. Remove 10 g from the glider and place it on the hanger. Repeat steps 4 and 5.
If times are again consistent repeat this procedure until all 40 g originally placed
on the cart are on the hanger.
7. Use the balance to find the mass of all moving parts: the glider, hanger, string
and weights.
Calculations
We will use
v 2 2 = v 1 2 + 2aL

to find the acceleration for each weight where L is the distance between
the photogates. The velocities v 1 and v 2 are found by dividing the length of
the gliding cart l, by the time t 1 and t 2 respectively, taken to pass under
each photogate:
l
v
1
= and
t
1
v =
2
l
t
2
The force causing acceleration is given by F h = mg where m (expressed in
kg) is the total mass of the hanger and weights placed on it and g is the
acceleration of gravity (g = 9.8 m/s 2 ).
Table 1: Observations and Results for Newton’s Second Law
m h F h
l L
t 1 t 2 v 1 v 2
a
(kg)
(N)
(m)
(m)
(s)
(s)
(m/s)
(m/s)
(m/s 2 )
Analysis
Plot a graph of acceleration (y-axis) versus force (x-axis). Find the slope of
the best straight line through the points. The value of the slope is the
constant of proportionality between acceleration and force. Compare this
value to the reciprocal of the mass of the glider, hanger and the 40 g
masses as obtained on the balance.