Dynamics is a subset of mechanics, which is the study of motion. Whereas kinetics studies that motion itself, dynamics is concerned about the CAUSES of motion. In particular, it involves the concepts of force, momentum and energy. This video gives an overview of what dynamics is, and is useful as an intro to its study, or as a review
1. Understanding Newton's Laws
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Using the animation at pHET, I explain the three laws, starting at the 3rd, then the second and finally the first.
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An opportunity to play with the pHET animation yourself. Click the three dots to go full screen
2. 1st Law - a party trick
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This demo/party trick helps you understand the principles behind Newton's first law |
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3. The Third Law
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Newton's third law, often described as an action and reaction force, has often confused students. This video uses a horse and a cart to hopefully clarify understanding |
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4. The normal force, including inclines
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Check out this pHET interactive on Ramps, Forced and Motion. At this stage this will only work on computers and not iPads
5. Friction
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This fairly straight forward interactive demonstrates a fundamental principle behind friction - it's not due to physics contact of the surfaces, but at an atomic level, due to the electroweak repulsive forces. It is the irregularity of the surfaces that lead to friction
6. Forces in equilibrium
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Using weights and pulleys, a situation can be in equilibrium, where there is no net force. This video looks at the situation and helps you mathematically analyse the situation |
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There are a number of ways we can explore this concepts further.
One aspect of most high school physics course on kinematics, is that they only concern themselves with constant acceleration. In reality however, acceleration, like displacement and velocity, can chance with respect to time.
Velocity is the rate of change of displacement. Unit: m/s2
Acceleration is the rate of change of velocity.
So what is the rate of change of acceleration?
The answer to that is the jerk. So slope of the acceleration vs time graph is the jerk. Unit: m/s3
We can go further.
What is the rate of change of the jerk?
Well it's the snap. Unit: m/s4
Can we go further? Yep. The rate of change of snap is the crackle. Unit: m/s5
I think you can guess the next one.
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- Forces in equilibrium - Use this interactive to test your understanding. Set the weights, calculate the angles and see if you are correct
7. Pulleys not in equilibrium - Attwood's machine
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What if masses hanging on pulleys are NOT in equilibrium? This video will examine accelerating systems and how to solve them. It also includes inclined examples |
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