Physics 1 Lab report

Newton’s Laws Activities (copyright Doug Bradley-Hutchison 8/17) page - 1 -

Newton's Laws Activities Equipment: Logger Pro software Ultrasonic Motion Detector Pasco (non-friction) cart with extra masses Pasco Track Wooden Hammer 0-5N and 0-1N (sensitive) spring scales Note: Several files are available that can be used for motion detector related activities. Consult your instructor. Activity I

The Effect of Impact Forces Consider the motion of a cart that is placed about a meter in front of a motion detector and then set in motion towards the detector by an impact (say, as delivered by a wooden hammer). Several additional impacts are then delivered at regular intervals once the cart is in motion. Consider the velocity-time graph, and repeat the described process several times (if necessary) so as to produce results that can be clearly interpreted. You should be able to point out where each impact was delivered, and characterize the motion of the cart in between impacts. Sketch your best velocity-time graph below.

What effect do the impacts have on the motion?

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Characterize the motion of the cart in between impacts. That is, does there appear to be acceleration or is the motion closer to constant velocity. Activity II

How Force Affects Motion Consider two different hypotheses for describing the effect that an applied force has on the motion of an object: H1. The velocity of the object is directly proportional to the applied force. That is, V = C F where C is some constant. or H2. The acceleration is directly proportional to the applied force. That is, a = C F where C is some constant different from the previous "C". Pre-Activity Questions If force is directly related to velocity then the motion that results from the application of a constant (unbalanced force) will be at constant velocity. Describe the acceleration of an object that moves at constant velocity. On the other hand, if force is directly related to acceleration the application of a constant force will result in motion at constant acceleration. Describe the velocity of an object that moves with a constant acceleration. Discuss the answers above with the instructor before proceeding. Now consider the following procedure. You attach a sensitive spring force meter to a cart, place the cart on a level table about 50 cm away from a motion detector and then pull the cart along the table (in a straight line) away from detector. For some portion of (or most of) the motion you coordinate your movement so as to maintain a relatively constant reading on the force meter. Graphs are made of velocity-time, and acceleration- time.

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Don't Collect data yet. BEFORE YOU COLLECT DATA answer the following: Assuming you carried out the described procedure, describe (and/or sketch) the graphs that would be produced if H1 were correct.

Repeat, assuming H2 were correct.

Carry out the procedure. Be careful to apply enough force so as to clearly demonstrate its effect (the cart's motion should be relatively rapid). You’ll need a fairly long (six feet or so) smooth table top, like a lab table, and a clear path so that you can walk or perhaps run parallel to the table’s edge without tripping over chairs or other obstacles. You cannot do this experiment standing still! Have one member of your lab group attach the force meter to the motion cart and while keeping the meter nearly parallel to the table pull the cart along the table while keeping the reading on the force meter nearly constant. That is, the person pulling the cart needs to move with the cart in such a manner that the force reading stays constant. The force meter should read a mid-range value in terms of the meter maximum. The exact value is not so important, but you do not want to apply a constant force of zero Newtons.

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Describe/Discuss your actual results below. Which hypothesis appears to be correct? Include sketches of the relevant graphs. You should be able to decide between the two hypotheses based both on your observations of how the person pulling the cart was moving and based on the graphs.

Activity III

How Mass Affects Motion Initiating Vertical Movement: Attach one of the stiffer force meters (0-5N) to a cart and determine the minimum amount of force required to lift the cart slowly (avoid any jerky motions). Record the reading on the scale. Force required to lift the cart: ____ N Initiating Horizontal Movement: Place a cart on a level track (or table), and attach the sensitive (spring) force meter to it (0-1N). The attachment should be made so that the cart can be pulled along the track or table. By experiment, estimate the amount of force required to initiate horizontal movement of the cart. Record that value below. Force required to initiate horizontal movement: __________N Determine the ratio of the two force values: _______ (no units: ratio of two "like" quantities) Use the motion detector to examine how mass affects constant force motion.

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The system below consisting of a cart a light string and a hanging mass is acted on by a constant unbalanced force: the weight of the hanging mass. If a motion detector were placed behind the cart the motion of the system could be tracked. Note that you will get sufficient acceleration using a very small hanging mass (as little as 10 or 20 grams).Also note that the total mass of the system is the mass of the cart and the hanging mass together yet the unbalanced force is the weight of the hanging mass. You want to keep the unbalanced force constant, yet (see below) you will vary the mass of the system.

Study the motion of the system with no extra mass on the cart. Repeat until you have velocity and acceleration graphs that clearly show the motion of the cart and that can therefore be interpreted. Check with the instructor and then sketch the graphs on the axes below. Use Store Latest Run to save this data for comparison. Now double the mass of the cart by adding one of the mass blocks. Repeat the above exercise applying the same amount of constant force as before (same hanging mass). Sketch your results on the axes below. Discuss/Describe your results. What is the effect of mass on each of the motion variables graphed ? Be specific..