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# 12.5: Unit 8 Lab- Accelerated Motion

## Motion

### Materials:

• lab sheet and writing utensil
• calculator
• for distance learners, access to online forums, videos, and help features for the spreadsheet software will likely be necessary
• string
• 20 g mass with hook
• “frictionless” track + cart
• motion sensor + computer with sensor control and analysis software (self-tracking motion cart optional).

### Preparation

Before we begin creating and testing a hypothesis regarding forces and motion, we need to familiarize ourselves with basic motion concepts and the equipment we will use to measure motion.

First set up the motion sensor and analysis program so that it displays the position, velocity, and acceleration vs. time graphs of your motion as you move in front of the sensor.

Next, create each of the following graphs by moving in front of the motion sensor. Have your instructor sign off on each graph as you progress.

#### Constant Position

Create a constant position graph. Instructor signature:____________

Describe how you had to move to create this graph.

Describe the velocity and acceleration graphs created by your motion.

#### Constant Velocity

Create a constant velocity graph. Instructor signature:____________

Describe how you had to move to create this graph.

Describe the position and acceleration graphs created by your motion.

#### Constant Acceleration

Create a constant acceleration graph. Instructor signature:____________

Describe how you had to move to create this graph.

Describe the position and velocity graphs created by your motion.

## Accelerated Motion

Now we will use the cart and track to test a hypothesis about how position, velocity, acceleration and net force are related. Setup the cart and track and motion sensor (or the self-tracking cart) to measure the position, velocity, and acceleration of the cart as it moves down the track.

### Test Method

Now build the following setup in in order to use the force of gravity on a hanging weight to accelerate the cart. Use a hanging mass roughly 1/5 of the cart mass. The cart will run on a smooth track to minimize friction. (We know the track/cart setup is not completely frictionless, so we are making the assumption that the friction is small enough not to significantly affect our results). Measure the cart mass and record here (in Kg):

Measure the hanging mass and record here (in Kg):

### Observation

Gravity is acting on both the cart and hanging mass, but when the hanging mass isn’t there the cart doesn’t accelerate. Therefore it seems like only gravity on the hanging mass contributes to causing acceleration.

### Question

If only the hanging mass contributes to the gravitational force causing acceleration of the system, does the cart’s mass even matter at all?

### Hypothesis

If we include only the hanging mass in calculating the force causing acceleration, but include both masses in calculating the acceleration caused by that force, then we will (circle one):

Correctly predict the acceleration of the cart

Incorrectly predict the acceleration of the cart

### Test

According to our hypothesis, how big is the force causing acceleration of the system?

Use the force you found above and Newton’s Second Law to calculate the expected acceleration of the cart + hanging mass, using their combined mass as the system mass.

Use the force you found above and Newton’s Second Law to calculate the expected acceleration of the cart + hanging mass, using only the hanging mass as the system mass.

Using the same amount of hanging mass as in your calculations above, release the hanging weight + cart while measuring the position, velocity, and acceleration of the cart.

### Analyze

The force that is accelerating the cart + hanging mass system is the force of gravity on the hanging mass, which is constant. Should the measured acceleration also be constant? Is it constant? Explain.

Use the software to find the average value of the acceleration and record here:

### Conclusions

Which of your predictions is correct, the one that uses the combined mass for the system mass, or only the hanging mass as the system mass?