LAB: NEWTON ’s SECOND LAW  (F = ma )

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HOW CAN YOU INCREASE ACCELERATION?

 

The amount of an object’s acceleration depends on the mass of the object and the size of the object acting on the object. In this lab, you will learn what happens to acceleration when mass and force are varied. (F = m a). You will show that the acceleration is inversely proportional to the mass (for a given force). You will also show that acceleration is directly proportional to the force.

You will show that using graphs.

 

SKILLS: observing, measuring, graphing

 

MATERIALS: small cart              time sparker     pulley         C-clamps

                           masking tape         string               masses        graph paper.

                 

 

 

PROCEDURE

1. Use the medium C-clamp to secure the pulley to the edge of the table.

2. Tie a mass of  25 g to the string.

3. Attach the other end of the string to the cart. The masses should just touch the floor when the cart is against the pulley.

4. Tape the   paper tape to the other end of the cart. The paper tape has to go through the time sparker. The tape has to be as long as the table.

                                                                                

5. Pull the cart back until the 20g mass touches the pulley. Mark this position with a piece of masking tape. This is your starting line.

 

6. Move the car next to the recording timer. Release the car, allowing it to accelerate across the table top. Catch the car before it collides with the pulley or plunges to the floor. Torn off the recording timer. Remove the tape and inspect it. A dark area should occur at the beginning of the tape where the timer made numerous dots close together before the car was released. Note a series of dots, each an increasing distance from the previous one. It is in this interval of the tape that the cart was accelerating. Write 0 by the first distinguishable dot. Continue counting and marking dots 1, 2, 3, 4, 5 , and so on. After the mass hits the floor, the dots will clump together, indicating the end of the acceleration phase. Stop counting at a dot located about 10cm before the clump of dots.

 

7. Measure in meters the distance from zero dot to the chosen end dot. Record this distance in table 1. Record the number of dots to this end point in table 1.

 

8. Add 1 mass (100g) to the cart to increase its total mass. Repeat steps 6,7

 

9. repeat steps 6,7 , each time adding another mass to the cart.

 

10. Leave 400g on the cart. Attach only one mass to the string. Repeat steps 6, 7 , but this time record your measurements in table 2.

11. Add another mass to the string (10g) and repeat step 10.

 

 

11. Calculate acceleration for each of your measurement in table 1 and table 2.

 

12. Graph Make a graph of acceleration vs mass for the data in table1.

y = acceleration (a) and x = mass (m) . (find a smooth curve that best fits the data)

The independent variable is _______________

The dependent variable is the ___________________

The graph shows that the acceleration (your y) is __________ proportional to the _____ (your x)

You just have shown Newton’s second law: F = ma or a = ________ .

 

 

13. Graph Make a graph of acceleration vs force for the data in table2.

Acceleration = y and force = x. Trace the best fit line. What kind of relationship is this ?

The independent variable is the _____________. (the one you changed)

The dependent variable is the ________________.

Acceleration (your y) is therefore ____________ to the force (your x).

The slope is _______________.

Find the right units for the slope : __________________

Hints: units for force (your y ) = kg m/s/s  and units for acceleration (your x ) = m/s/s

Newton’s second law: F = ma so a = ___________

So the slope you found represent _____________

You can therefore use your graph to find the mass (or inertia of an object).

Find  the % difference between the computed mass using the graph and the true mass:

:

% error = (true mass - computed)/ true x 100

 

14. What are the two factors that affect the acceleration of an object?

Was the goal of the lab achieved ?

 

 

 

 

 

 

 

TABLE 1

TABLE 2