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Old Nov 1st 2017, 07:33 AM   #1
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Harry Potter Physics

I was watching a Harry Potter movie. Harry Potter movies are great. In the movie Hermione says "Wingardium Leviosa" pointing her wand at an object and that object levitated. It moved straight up. This I think violates the laws of physics.

I think it violates the third law of newton. For an object to move up thrust is required. A rocket moves up due to thrust and as the gases are pushed downward the rocket moves upward. The third law of newton is at work here. It states: For every action, there is an equal and opposite reaction. Same goes for a bird flying. A thrust moves the bird upwards. This thrust is provided by the down stroke.

My question is that according to me the above is correct but what if you throw a ball in the air? Is thrust also provided to the ball?
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Old Nov 1st 2017, 09:50 AM   #2
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Originally Posted by avito009 View Post
I was watching a Harry Potter movie. Harry Potter movies are great. In the movie Hermione says "Wingardium Leviosa" pointing her wand at an object and that object levitated. It moved straight up. This I think violates the laws of physics.
Well, yes, of course it does! It's magic- and magic, pretty much by definition, violates the laws of physics.

I think it violates the third law of newton. For an object to move up thrust is required. A rocket moves up due to thrust and as the gases are pushed downward the rocket moves upward. The third law of newton is at work here. It states: For every action, there is an equal and opposite reaction. Same goes for a bird flying. A thrust moves the bird upwards. This thrust is provided by the down stroke.

My question is that according to me the above is correct but what if you throw a ball in the air? Is thrust also provided to the ball?
Obviously if you throw a ball in the air, you arm provides the thrust.
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Old Nov 1st 2017, 10:18 AM   #3
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Originally Posted by avito009 View Post
I think it violates the third law of newton.
I read a lot of sci-fi books and my dad left me a bunch from the 60's and 70's. Authors like Fredrik Pohl, Arthur Clarke, Isaac Asimov, and Ray Bradbury along with other notables. In many of the space stories you have what is called a "reactionless drive." It violates Netwon's 3rd very badly. (In fact the supposed EM drive in the news in the last couple of years is supposed to do this.) It's not just Harry Potter...The idea has been in a lot of sci-fi.

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Old Nov 1st 2017, 10:38 AM   #4
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For an object to move up thrust is required.
I don't think so.

That would be a direct violation of Newton's First Law.

The body starts with an initial upward velocity and continues to move upwards with no subsequent thrust but decelerating until it reaches zero velocity.

That is a direct result of Newton's first and Second laws.

Obviously if upward thrust is applied the body will go further.
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Old Nov 1st 2017, 06:19 PM   #5
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Since we are talking magic, one can indulge the imagination...

In quantum physics the position of an object is probabilistic.
The magic is altering the probability of the object being in what would otherwise be a low probability location.
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Old Nov 2nd 2017, 12:50 AM   #6
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Newtons laws violation

After looking at studiots comments I think all the three laws of newton are being violated in this case. But how?

Newtons first law states An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external force.

Now initially the object is at rest then it moves up due to the force of the wand. So the object at rest should remain at rest if there is no force but here there is a force, the force of magic. It is due to this force of the wand that the object moves. Now when this wand stops its motion the object is held in air and is stationary. Here newtons third law applies. To stop or slow down an object, a force must be applied in the direction opposite to that of the objectís motion. Exerting a force results in an equal force in the opposite direction. This force in the opposite direction is the wands force.

Newtons second law is also not violated F=ma. The force of the wand is 10 newton because the objects mass is 2kg and acceleration is 5 m/s^2 which is 10 newton and this force is provided by the wand.
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