100 POINTS! BRAINLIST! PL I NEED HELPPP Now that you know how forces affect the motions of objects, you can use the Tracker video analysis tool to create dynamic models for a wide range of physical situations.
Tracker enables you to create two different types of mathematical models: analytical and dynamic. An analytical model enables you to enter mathematical expressions for x and y positions as a function of time. That’s sometimes useful, but from a physics perspective, a dynamic model is much more flexible and powerful.
A dynamic model enables you to set the initial conditions for a particular system (initial positions and velocities); then you can mathematically define any forces acting on that system. Once those are set up, the model acts like an object in space, responding to the forces you’ve imposed on it. It can continue moving forever, if that’s what the forces would do to an object in real life. By visually matching a marker for your model to the real motion on the video, you can define and refine a mathematical model for a wide range of real-world situations.

In the first two tasks of this Unit Activity, you’ll create dynamic models for motions in both one and two dimensions.

Activity Research – Creating a Dynamic Particle Model
Before you begin, do a little research and find out where you can get help in creating your models. In Tracker, you can always access illustrated help to do anything. In Tracker, you can always access the illustrated Help dialog (? In the Toolbar).

For this project, you’re going to need to check out the Tracker Help instructions for Dynamic Models. You can print this Help document, but it is available from Tracker anytime you need to refer to it.
For this project, you’re going to need to check out the Tracker Help instructions for creating a dynamic model.

Instructions – Building your Dynamic Model
Start your activity by opening this Tracker experiment: Ice Slide 2 model man.

Click play to watch the video. The other video controls allow you to rewind the video or step forward or backward one frame at a time.

In this activity, you’ll define a dynamic model for the motion of an adult sliding on ice. In the Ice_Slide2_model, a blank model setup is already in place for you. The file also has the man’s motion tracked with point mass Ice Slide 2.

For this one-dimensional motion, the vertical force of gravity and the normal force balance out. Although there is some air drag, the only significant force on the sliding man is kinetic friction. Review, if necessary, the force relationship for kinetic friction.

A dynamic model is already started for you in this file. Follow the two steps in the screen captures below to open the model setup and begin your modeling work.

parameters – Enter the man’s mass (displayed on the first frame of the video)
initial values – Enter those that apply to this x-direction motion: t, x, and vx.
force functions – Enter a function formula for kinetic frictional force in the x direction. (Hint: Use 9.81 for the acceleration of gravity in your formula.)

Part A
Once you’re satisfied with your model, record your model values in the table below.

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Part B
Describe how well you think your modeled position matches the observed position for the man.

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Part C
Next, you’ll compare your model for the man with your model for a boy sliding on the same sled along the same path. Keep the first Tracker experiment open, but also open this Tracker experiment: Ice Slide 1 model.

From this file, select the point mass model boy and repeat the procedure you used to create the dynamic model for the man. Once again, use the initial values for time t = 0.20 seconds.

Try different values of the coefficient of friction and come up with a model that matches the motion of the child. Once again, modify the value of mk to get as close as you can to matching the boy’s observed position for the entire slide.

Once you’re satisfied with your model for the boy, record your model values in the table below.

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Part D
Describe how well you think your modeled position matches the observed position for the boy.

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Part E
Look at your recorded results and models for both the man and the boy. How close are the coefficients of friction for the sled on ice for the two runs? How confident would you feel about specifying a coefficient of kinetic friction for this sled on this ice surface, based on these results? Support your conclusion. What other variables might impact this coefficient result?

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Part F
Finally, observe the values of horizontal acceleration for the point masses and the dynamic models for the man and the boy. What can you say about the acceleration?