Newton's Second Law E-practical
Introduction
Newton’s second law is perhaps the most well-known principle in Physics. Galileo came close to finding it, but it was Newton who finally nailed it as the force, F, acting on a body of mass m, causes an acceleration, a, where they are related by:
F = ma
We are quite used to this principle in our everyday lives. Driving a car, if we push harder on the accelerator then the engine produces more force on the wheels and the car accelerates.
This law something that we can confirm with the airtrack by applying a series of different forces to the glider and measuring its acceleration using the photogate timers.
Introduction to the Airtrack
The airtrack is a very useful device for performing a variety of experiments about motion, forces and momentum. What makes it so effective is its use of pumped air to create a virtually frictionless track upon which various glider configurations can be put in motion and collided against.
The glider has a long strip of white card that interrupts a light beam as it passes through the photogates, this allows its passage to be timed from which its velocity can be calculated.
Realistic experimental technique
E-practicals are 3d, highly realistic emulations based on a blend of theory and the actual practicals, giving an authentic experience of doing the actual practical in a laboratory. Students operate the apparatus, make measurements and obtain their own results. It is designed to reproduce the experience of performing the practical rather than simply demonstrating the underlying physics. Like a real experiment, it can be done badly. Careless setup or measurements can produce poor results, so students have to apply experimental technique and take care with their measurements.
Works directly in a browser
No installation is required. Windows, Mac and suitable mobile devices can run the WebGL e-practical.
See it in Action
This shows how the e-practical can be used. In particular it shows how the student or teacher interacts with the apparatus and how the interaction can be controlled using the mouse or the alternative on-screen controls.
What students do
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With the glider to the left of the first gate, mark its position so repeat runs can be made from the same place. Start by using the lightest weight.
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Using the paired timer gates (these are the ones that the simulation starts with) time how long it takes for the glider to go from the first timer to the second. Note this time as Dt.
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Using the non-paired timer gates (with the glider out of the way, click on the large red cube at the left of the simulation). Let the glider go from the same position and note the time it takes to go through each timer. Note these times as t1 and t2.
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Repeat this for various weights.
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You can add weights to the cradle by placing the mouse cursor over the cradle and using the mouse wheel.
Complete the table:
Plot the weight (Mass X g) on the x-axis and the acceleration on the y-axis and you should obtain a straight line.
What you get
The application is supplied as a PowerPoint which provides background, a synopsis of what the student will learn, a description of the Physics involved, a description of the apparatus, the independent and dependent variables, the method, a link to the interactive online e-practical, analysis of the results and further discussion.
E-practical
Runs in a modern web browser. No software installation required. Recommended or desktops but will run successfully on tablets of medium to large size with a browser that supports WebGL.
School/Department licence £9.99
Valid for 1 year
This section is adapted from material developed by Dr Robert Lucas and is related to the book High School and Undergraduate Physics Practicals, published by CRC Press.