HIGHER COLLEGES OF TECHNOLOGY
ENGINEERING TECHNOLOGY DIVISION
MATHEMATICS & NATURAL SCIENCE DEPARTMENT
PHY-1103 LAB 2: NEWTON’S SECOND LAW
Instructions:




The lab is a team work and participation of all the members of the team is compulsory.
Lab report must be typed.
Late submission of the report will cause deduction in marks.
Academic honesty has to be maintained while doing the lab.
Submission Date:
………………………………………………..
Objective of Evaluation
1
2
3
4
Report presentation (must be typed)
5
Record of observation as tabulated data
19
Graph plotting
20
Analysis, evaluation & conclusion
6
Total
50
Student Name
1
2
3
4
5
Max. Marks
Obtained
Marks
Student ID Number
Objectives
 To investigate the relationship between the acceleration and resultant force for an object
of fixed mass.

To determine the mass of the object using the force against acceleration graph.
 Compare the experimental value for the mass of the object with the actual mass.
Theory
According to Newton’s first law, an object remains stationary or moving at a constant velocity
unless acted upon by a resultant. Now, if there is a resultant force acting on the object, it will
accelerate. This means its velocity will change, either the speed or direction will change, and the
acceleration is directly proportional to the resultant force. This is known as Newton’s second
law of motion and is often written as
F  ma
(1)
where F = the resultant force in newtons,
m = mass in kilograms, and
a = acceleration (m s–2).
In this lab you will investigate this relationship for a car (trolley) of a fixed mass mc kg using the
apparatus shown in figure 1 below and an automatic device to measure the acceleration.
Car / trolley of mass, mc
String
Pulley
Friction-compensated track
Laboratory bench
Hanging mass, mh
Safety mat
Figure 1: Illustration of the setting up of apparatus.
You will vary the applied force by changing the hanging mass mh kg. Assuming that the pulley
is smooth, the force on the car (trolley) is the weight of the hanging mass mh. Then the force is
calculated using
W = mhg
(2)
∑
𝐹⃗ = (∑ 𝑚) 𝑎⃗
𝑒𝑥𝑡𝑒𝑟𝑛𝑎𝑙
𝑚ℎ 𝑔 = (𝑚𝑐 + 𝑚ℎ )𝑎
𝑎 = 𝑔𝑚
(3)
𝑚ℎ
(4)
ℎ +𝑚𝑐
or,
𝑎
𝑚ℎ = 𝑚𝑐 𝑔−𝑎
(5)
2
where W = weight of the hanging mass in newtons
mh = hanging mass in kg
g = acceleration due to gravitational force which may be considered as 9.8 N/kg
Since equation (1) is in the form of y = bx which is the standard form of a straight line through
the origin, a graph of hanged mass mh (y-axis) against acceleration ratio a/(g-a) (x-axis) is
expected to give a straight line through the origin. The gradient of the graph provides the
experimental value for the mass of the car (Equation 5).
To assess how close these values are to the actual value of the mass of the car mc, we can
calculate the percentage difference using
Percentage Difference =
|actual value − experimental value|
actual value
× 100
Apparatus
1.
2.
3.
4.
5.
6.
7.
8.
Friction compensated surface or air track;
Car or trolley;
Smooth pulley;
Mass hanger and slotted masses;
String;
Light gate(s) with data logging system;
Safety mat;
A piece of paper with the mass of car (or trolley) written on it. This is the actual value of the
mass of the car (or trolley).
Procedure
1. Set up the apparatus as shown in figure 1.
2. Remember to keep the safety mat directly under the mass so that it will prevent the mass
from hitting the floor.
3. Use the MODE button on the data logger to get on the screen ACCELERATION.
4. Then use the SELECT button to get on the screen TWO GATES.
This means that you will be measuring the acceleration of the car between the two light
gates.
5. Press the START/STOP button on the data logger.
6. At this stage call the teacher/technician to check that you are on the right track.
7. Hang a mass as mh, e.g. 20 grams. Record the mass in table 1.
8. Released the system from rest. Record in table 1 the acceleration measured from the data
logger.
9. Repeat steps 7 and 8 for the same mass and calculate the average acceleration.
10. Continue the experimental by varying the mass from 20 g to about 80 g in steps of 5 g.
3
Observation
1. Measured mass (actual mass) of the car mc: ………………………….
(4 marks)
2. Complete the table below by varying mh
(15 marks)
𝑎
𝑔−𝑎
Acceleration
mh
(
(
Avg. a
)
(
)
a1
a2
)
a3
Graph
3. Draw a graph of hanged mass mh (y-axis) against acceleration ratio a/(g-a) (x-axis) in
Excel.
(4 marks)
4. Label your axes with the correct quantities and correct units.
(3 marks)
5. Draw the line of best fit (trend line in Excel) for your data.
(3 marks)
6. Write down the equation of the best fit line (trend line).
Equation:
…………………………………………………………………
(4 marks)
7. Record the gradient (slope) of your line.
Gradient (slope) of the line:
……………………………………
8. Insert a screen shot of your graph from Excel
4
(3 marks)
(3 marks)
Analysis, evaluation and conclusion
9. Using the slope (gradient) of your graph find the mass of the car.
(3 marks)
10. Calculate the percentage difference of your value for the mass of the car compared with
the actual mass of the car / trolley.
(3 marks)
5