Projectile Motion

Practice Newton Forces

Homework due November 7th, 2012

Homework due November 5, 2012

Lab Assessment F=ma

Analysis part 1.

Acceleration (m/s2)	Force Applied (N)
0.4	0.4
0.8	0.8
1.2	1.2
1.6	1.6
2.2	1.9

The linear relationship tells us that the larger the net force is, the larger the acceleration will be.

Questions

1)    The slope of the line should indicate the mass of the cart.

a.    Explain why the slope is the mass. Show also that the units of the slope correlate with the units of the mass.

The slope represents the mass because of the format of the equation. The original equation for the Net Force is: F_app - F_friction = mass*acceleration. Solving for F_app yields to: F_app = mass*acceleration + F_friction. This is in slope-intercept form, y=mx+b where ‘y’ represents F_app, ‘m’ represents mass, ‘x’ represents acceleration and ‘b’ represents F_friction. You can verify that the slope represents the mass by considering the units of the y-axis and the x-axis. Y(N)/X(m/s²) à Y(kg*m/s²)/X(m/s²) à kgm/s² * s²/m = kg

b.    What is the slope? What is the actual mass? Find the experimental error.

Slope = .8525kg

Actual Mass = 807g = .807kg

Experimental Error = 5.3% error

c.    We don't expect more than 15% error. Identify at least two solid reasons for the error.

·         Wheels not balanced

·         Friction between string and wheel

·         Force of friction along table wasn’t constant

2)    The y intercept is the force of friction. Explain why! what is the average force of friction as seen on your graph.

The y-intercept is the force of friction because it always exists, even when there is no force pulling the cart. Therefore at 0N of force, friction still takes place. The average force of friction was approximately 0.123.

3)    The friction force you found in 5 is only the average force. Use the smallest force (least acceleration) and largest force (highest acceleration) to compute from an equation the friction force in each case. Which one seems to be larger? Do you expect this result.

Smallest force (least acceleration) à .4 = .8525*.4 + b à b = 0.059N

Highest force (most acceleration) à 1.9 = .8525*2.2 + b à b = 0.0245N

The smallest force yields a larger force of acceleration. I expected this to happen because the force of friction tends to have more of an impact on an object with less applied force. Possibly, the more force you apply on an object the less of an impact the force of friction will have.

                                           

Analysis for part 2

Mass (g)	Acceleration (m/s2)
807.2	1.8
1307.2	1.3
1807.2	0.9
2307.2	0.7
2807.2	0.6
3307.2	0.5

1)    What kind of relationship do we expect?

Inverse relationship

2)    Does this relationship agree with Newton's second law which is
Force_net = ma or a=F_net/m

YES! The equation we got was y=929.51/x^.926

In this equation, ‘y’ represents acceleration, 929.51 represents the F_net and ‘x’ represents the mass.

Conclusion

With the help of toy cars, weights, sensors and computers we were able to model the type of work Isaac Newton did to derive the famous equation F=ma.

To show the relationship between Force and Acceleration, we increased the applied force on a toy car and using sensors determined its acceleration. Performing five consecutive tests with increasing forces we concluded that there is a direct positive relationship between the F_app and the acceleration. Plotting (acceleration, F_app) as coordinates we produced a best-fit line that gave us the direct relationship between the ‘y’ (force) and ‘x’ (acceleration). The equation was in the form of slope-intercept, as expected, because the equation represented F_app = mass*acceleration + F_friction. Comparing the slope-intercept form of an equation with that of F_app we concluded that the slope of the line represented the mass. We verified this using the slope formula (change in y / change in x), which yielded N/(m/s²) = kg.  The setup of our experiment was prone to many errors in calculations, such as: unbalanced wheels on carts, change of friction on surface, friction between string and wheel (that the weights were attached to).  In future experiments we should strive to eliminate as many errors as possible so our results can be more accurate.

We were also able to show that Mass and Acceleration have an inverse square relationship, as Newton stated with his formula a=F/m. We performed the same tests as in the first experiment; however this time the applied force remained constant and we altered the mass on the toy cart. Using the same sensors we determined the acceleration while using 5 different masses, and the graph produced was indeed that of an inverse square relationship. The form of the equation we received was y=k/x, where ‘y’ represents the acceleration, ‘k’ represents the constant force and ‘x’ represents the mass.