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Newton's Second Law: Physics Lab

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  • 0:01 Newton's 2nd Law
  • 0:44 Physics Lab Steps
  • 2:24 Calculations and Conclusions
  • 3:57 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this lesson, you will be able to explain Newton's 2nd Law and use real-life evidence to show that the basic ideas behind the equation are correct. A short quiz will follow.

Newton's 2nd Law

Newton's 2nd Law says that larger objects take greater forces to accelerate them. It is best described using the equation F = ma, where F is the net force applied to an object measured in newtons, m is the mass of the object measured in kilograms, and a is the acceleration of the object in meters per second squared.

The basic idea is that if you apply more force to an object, it will accelerate more. But that acceleration will be smaller if the object has a larger mass. Today we're going to try to confirm this equation using an experiment. Experiments are always limited by how accurate we can be with our measurements, and other factors, like friction, but if we're very careful, it's possible to check if the equation is at least approximately correct. Time to investigate!

Physics Lab Steps

For this physics lab, you will need:

  • A flat-bed, wind-up toy car
  • A series of weights that will fit onto the back of the toy car
  • A stopwatch
  • A tape measure or ruler
  • Duct tape
  • And a surface that's as smooth as possible

Step 1: Mark a starting position on your surface for the toy car, using the duct tape. For best results, mark the position of at least two of the wheels.

Step 2: Mark a final position a few meters from the toy car's starting position.

Step 3: Without any weight, get an assistant to wind up and release the toy car in position.

Step 4: Use your stopwatch to measure the time it takes for the toy car to travel between the two positions you marked. You should start the stopwatch when the back of the car reaches the start of your measured position and stop the stopwatch when the back of the car reaches your final mark.

Step 5: Note down the time you recorded on your stopwatch and repeat at least five times.

Step 6: Add the next smallest weight to the back of the car. You may need to tape it down using the duct tape, but if you do, make sure to measure the mass of the duct tape when you're done taking data.

Step 7: Repeat your five measurements with each of the weights.

Step 8: Weigh your car, and any duct tape, so that you know the total weight of the car during all your time measurements.

You should create a data table. Your measurements are the distance you marked along the ground in meters, the mass of the car in kilograms (including the car, all weights, and duct tape), and the time measurements you took in seconds. You can then create an average of each set of five trials by adding them up and dividing by five. Once you have your data, it's time to do some calculations.

Calculations and Conclusions

First, we need to calculate the average speed of the toy car between the two marks. Do this by taking the distance between the marks and dividing it by the average time of each set of five trials. You will then have an average speed for each of the masses of car.

Plot a graph of average speed against mass. The axes should look something like this:

Graph for example
graph of speed vs mass

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