The goal of this lab is to determine the acceleration of an object in free-fall the most straightforward way: just dropping it.

In order to get an accurate time measurement, you need to drop an object from a significant height. We are going to drop an object from the balcony on the stairway between the science wing and the math wing.

##### Roles
• One person needs to drop the tennis ball.
• One person needs to measure the time it takes to reach the ground.
• One person needs to stand the doorway and make sure nobody is coming.

### IMPORTANT SAFETY NOTE

When you are doing this lab, somebody MUST be standing in the doorway at the bottom of the stairs and making sure nobody is coming when the tennis ball is dropped. If nobody is doing this, it is very unsafe. Don't ever ever ever drop something off the balcony without first making sure no one is coming.

Also, please don't very fast throw the ball around. There's a security camera right there, and you don't want to be on film throwing fastballs at each other!

##### Steps
1. Measure the height to the top of the balcony from the floor. You should be able to do this with only a ruler!
2. Drop the tennis ball from the balcony, and measure the time from the moment it leaves the hand of the person dropping it to the moment that it strikes the ground.
3. Repeat this process 5 times, to get 6 measurements of time:
1. Was any of your measurements of time an outlier? An outlier is a measurement that is very different from the others. If there was an outlier, it was probably an error. Delete that measurement and repeat it.
2. Determine the average of your six measurements. Consider this to be the time necessary for a ball to reach the ground.
3. You are trying to find the acceleration of the tennis ball. You know three quantities, its displacement, its time interval, and its initial velocity. Pick one of the four kinematic equations to figure out the acceleration.
$$v_f = v_i + a \cdot \Delta t$$
$$\Delta x = v_i \cdot \Delta t + \frac{1}{2} a \left( \Delta t \right)^2$$
$$\Delta x = \left( \frac{v_i + v_f}{2} \right) \Delta t$$
$$v_f^2 = v_i^2 + 2 a \cdot \Delta x$$

 Looking For Formula Already Know Answer in a complete sentence with unit.
4. You know that the measurement you "should" get is 9.8 m/s2. Determine the percent error with the following formula: $$\text{% error} = \left| \frac{\text{Measured Value} - \text{Predicted Value}}{\text{Predicted Value}} \right| \cdot 100$$
5. Write at least two sources of error in this calculation.
6. Write two practical possibilities for how to reduce the error in this calculation. Practical means that nobody would be injured and you already own the equipment needed, or it would cost less than \$100.