Levitation Homopolar Motor
A) 3 Laws of Motion
1st Law: Law of Inertia
If ΣFnet = 0, a = 0
This means the object is either:
At Rest OR Constant Velocity
Explain this using Newton's 1st Law:
Why doesn't the ball roll backward after the cart stops and starts up again?
Notice that at the exact moment the ball reaches the front of the cart, the cart instantly moves ahead at the same velocity it had previously. Therefore the ball never actually comes to rest. It maintains its 'moving inertia'.
If there had been even the smallest time interval between when the ball reached the front of the wagon and when the wagon began moving again we would have had different results. The ball would have bounced off the front of the wagon and when the wagon continued forward, the ball would then have rolled to the back of the wagon at an even faster rate.
Tip: Observe the animation again, but this time follow the movement of the ball with a ruler and you will see that once the ball starts moving, it never really stops moving relative to the ground.
Free Body Diagrams
Example: Block being pulled to the right at a constant velocity
Crucial Concept
A force is not required to MAINTAIN motion.
Let's Practice
A 5.0 kg box is moved across a floor with a horizontal Force of 12 N at a constant velocity. What is the force of friction on the box?
ΣF = ma = 0 // Because velocity is constant, acceleration is 0
ΣF = Fapp - ffriction
0 = Fapp - f
0 = 12 N - f
f = 12 N
"There's a big difference between knowing the name of something and knowing something."