Rotational Kinematics lab

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1. Use the velocity components to determine the direction of the velocity vector. Is it in the expected direction? 1. From the x-t and y-t images, the two curves show a sine and cosine relationship, indicating that the object is in uniform circular motion. Since position over time behaves as a sine and cosine function, this means that the velocity is their derivative, and the direction of the velocity is always perpendicular to the direction of the radius, so the velocity vector varies in the tangential direction, which is consistent with the theory of circular motion. The formula used to calculate speed 2. Analyze enough different points in the same video to make a graph of the speed of a point as a function of distance from the axis of rotation. What quantity does the slope of this graph represent? In this experiment, we investigated the relationship between radius, linear velocity and acceleration in uniform circular motion by analyzing the motion of three different points on a r...
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Car Pulled by Rope

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This is when we did the experiment.

Experimental data

Experimental and calculated data

The formula used to calculate speed

How do the predicted velocity and the measured velocity compare in each case?  Did your measurements agree with your initial prediction?  If not, why? 
  • I calculated the magnitude of v using the formula I worked out in class and found the prediction V to be much larger than the magnitude of v I did in the lab. Their percentage difference ranged from 26% to 74%. This could be due to the fact that the formula does not involve friction or air drag, or it could be due to measurement errors in the experiment.

Does the launch velocity of the car depend on its mass?  The mass of the block?  The distance the block falls?  Is there a choice of distance and block mass for which the mass of the car does not make much difference to its launch velocity?
  • From the velocities obtained from the experiment and the formula. If the mass of the block (Ma) and the distance dropped (d) are greater then the velocity will be greater, possibly because the longer d is, the more v is affected by the acceleration. The mass of the block (Ma) = Ma * g. If Ma is greater, more force will be applied. However, if the mass of the cart (Mc) is greater, then the speed will decrease, possibly because of the friction of the wheels on the surface.

If the same mass block falls through the same distance, but you change the mass of the cart, does the force that the string exerts on the cart change?  In other words, is the force of the string on object A always equal to the weight of object A?  Is it ever equal to the weight of object A?  Explain your reasoning.

The formula for calculating T

  • The tension T can never be exactly equal to the weight of the block. According to my formula, the amount of rope tension T actually depends on both the mass of the cart, Mc, and the mass of the block, Ma.


Was the frictional force the same whether or not the string exerted a force on it?  Does this agree with your initial prediction?  If not, why?

The formula for friction

  • In this experiment, friction does not behave in a static manner, but changes as the state of the system changes. As the rope exerts a pull on the cart, the friction force becomes more of a greater force (this can be deduced using the formula).



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