If you look up the equations for "elastic collisions" in physics you'll see that if you throw a ball with momentum p and it hits a sail with the same mass as the ball, this will cause the ball's momentum to drop to zero while the sail gets the same momentum p the ball previously had. But if you throw a ball at a sail that's vastly more massive then the ball, the ball actually rebounds with momentum -p while the sail's momentum increases by 2p, twice that of the ball thrown at it! I think that's basically what's going on here, if the fan imparts momentum p to some chunk of air the fan is pushed back with -p, so if the sail only gets momentum p there's no net movement of the connected fan and sail, but the sail is larger it can get momentum closer to 2p so there is net movement.
@Krazed2Kraze This looks similar to the horse and wagon theory. Where in theory the Horse and wagon which are connected should cancel it other out because of Newton's third law, but because the horse is also pushing on the ground and the ground pushes with equal force to move both the horse and cart. Not only that but what Grant describes sounds like a bounce, as in a light object being pushed away from the massive object after the light object ran into it.
Ok, question regarding this. The cancelation is because fan the pull the air from behind and pushing it forward, so the net energy is the same, but what if they had a fan that pulled it from the front and had the air go through a 180 degrees bent tube into the sail, so it's pulling from the front and blowing towards the front?
@@Drokkstar_ no, it doesn't matter which side the air is picked up from. If you draw the free body diagram, it only matters that the air molecules are relatively immobile and are given some forward speed.
Mythbusters got the explanation all wrong. First of all, air molecules don't "bounce" off surfaces like some have suggested. They create flow fields and pressure gradients. If you assume that all the force acting on the propeller is in the opposite direction of the air flow it generates, it still wouldn't matter if all the air was redirected backwards from the sail, the forces would cancel. The part that is being neglected is the propeller. The propeller isn't just colliding with the air causing it to flow, the rotation and shape of the blades cause a pressure differential (Bernoulli effect) that causes the air to flow and give it linear kinetic energy. Part of the force acting on the propeller is opposite the direction of the air, but the Bernouli part is (at least partially) counter the rotational moment of the blade. For this reason, the linear force acting on the propeller could be smaller than the force pushing on the sail. You can think of the sail in terms of drag force. In this case, the larger the sail, the larger the drag force at least until you reach the maximum force produced by the air flow. Newton's laws are not violated.
As a mechanical & aeronautics engineer I can tell you that you're mostly wrong. By your logic, the air behind the sail is moving faster, so it would have lower pressure (the air in front of the sail is not moving at the start) so it would push the sail backwards. But it obviously doesn't. Also it doesn't matter how the fan is pushing the air forward. It doesn't matter if it has a horizontal propeller or if it's a different kind of pump style. Study the free body diagram.
Contrary to Mythbuster’s contention, the operative principles involved here are not “thrust” nor Newton's third law-“For every action, there is an equal and opposite reaction”. Anyone with a basic knowledge of aerodynamics, such as airplane pilots or those who’ve read a book on basic sailing theory, understands that the force causing the boat to move forward or backward is “lift” resulting from a low pressure area. Granted, the momentum of air striking an airfoil, such as a sail, has some “thrust” effect upon the airfoil; however, the “thrust” is negligible compared to the lift resulting from low pressure on the lee side of the airfoil (sail) or propeller. It is Bernoulli's principle which is operative here. Bernoulli's equations provide that within a horizontal flow of fluid (such as air), where the fluid has a higher speed there will be less pressure than where the fluid is moving at a slower speed. If you view the Mythbuster’s experiment from the perspective of air speed and consequent low pressure areas, rather than the 'thrust' of air molecules, then you can see why the boat moves in the directions it does. When the aggregate of the low pressure areas on the lee side of the sail is greater than the aggregate of the low pressure areas on the upwind side of the propeller, the lower pressure on the lee side sail will pull the boat forward. Conversely, when the propeller is oriented in such a way that the air doesn’t flow sufficiently quickly around the sail (insufficient low pressure), then there is not enough “lift” to pull the boat forward. On the other hand, when the boat moves backwards away from the sail, this is caused by the propeller’s lift being greater than the sail's lift, acting like an airplane’s propeller. In other words, the sail and propeller are in a tug of war, with the greater (cumulative) low pressure lift vectors being the 'pull' that determines which direction the boat moves. I’ve never had a physics course or studied math beyond the 10th grade of high school (which I flunked twice before passing), so I’m sure an aerodynamics engineer could explain the operative principles here more precisely. Nevertheless, it seems to this layman, the application of Newton’s third law (equal & opposite) and “thrust” is largely irrelevant here.
Bernoulli's Principle is derived from applications of Newton's third law. Newton was slightly prior to Daniel Bernoulli, and the latter studied Newton's works. Bernoulli's Principle just describes a particular situation of a Newton's third law application. Furthermore, even if you study Archimedes principle, which is far prior to Isaac Newton, it is still just an application of the third and the second Newton laws. Newton's law is far more general. If you know the masses and the forces, it might be applied to any situation in any scale short from quantum dynamics, so it is never irrelevant.
As a mechanical & aeronautics engineer I can tell you that you're mostly wrong. By your logic, the air behind the sail is moving faster, so it would have lower pressure (the air in front of the sail is not moving at the start) so it would push the sail backwards. But it obviously doesn't.
Rip Grant Imahara.
If you look up the equations for "elastic collisions" in physics you'll see that if you throw a ball with momentum p and it hits a sail with the same mass as the ball, this will cause the ball's momentum to drop to zero while the sail gets the same momentum p the ball previously had. But if you throw a ball at a sail that's vastly more massive then the ball, the ball actually rebounds with momentum -p while the sail's momentum increases by 2p, twice that of the ball thrown at it! I think that's basically what's going on here, if the fan imparts momentum p to some chunk of air the fan is pushed back with -p, so if the sail only gets momentum p there's no net movement of the connected fan and sail, but the sail is larger it can get momentum closer to 2p so there is net movement.
+hypnosifl "But if you throw a ball at a sail that's vastly more massive then the ball" What is more massive the sail or the ball?
@@giantmiller1136 the sail, the air molecules are tiny.
Mitchell Street
0:43 then what is the point in the sail? just use the propeller instead? its not the same
Kilback Club
@Krazed2Kraze This looks similar to the horse and wagon theory. Where in theory the Horse and wagon which are connected should cancel it other out because of Newton's third law, but because the horse is also pushing on the ground and the ground pushes with equal force to move both the horse and cart. Not only that but what Grant describes sounds like a bounce, as in a light object being pushed away from the massive object after the light object ran into it.
Fausto Crossroad
There comparing the thing there doing with a sailing boat -_- note to self to different things might look similar but ain't :'p
Suck!!!
Woah there
Wouldn’t you get more energy if you just spin the motor in the opposite direction and ditched the sail
So basically a seaplane.
Ok, question regarding this. The cancelation is because fan the pull the air from behind and pushing it forward, so the net energy is the same, but what if they had a fan that pulled it from the front and had the air go through a 180 degrees bent tube into the sail, so it's pulling from the front and blowing towards the front?
My thoughts exactly. No one has tried this... seems odd. It’s either crazy stupid or crazy brilliant.
@@Drokkstar_ no, it doesn't matter which side the air is picked up from.
If you draw the free body diagram, it only matters that the air molecules are relatively immobile and are given some forward speed.
Newton was wrong! My mind... It is blown.
Questão do enem rs
hard to believe two out of the three people here are dead now
Only Grant is dead, who else?
@@joehill4094 That is not the woman in this video though. The woman in this video is Kari Byron.
@Calvinios
Watch the whole episode. They tested the resistance. Resistance on water was twice that of the wheels.
@Calvinios
Nope, the boat has much more resistance on water than those wheels have on solid ground.
Physics Be like
Physics be like
Mind=Blown
troll science at its finest..
Mythbusters got the explanation all wrong. First of all, air molecules don't "bounce" off surfaces like some have suggested. They create flow fields and pressure gradients. If you assume that all the force acting on the propeller is in the opposite direction of the air flow it generates, it still wouldn't matter if all the air was redirected backwards from the sail, the forces would cancel. The part that is being neglected is the propeller. The propeller isn't just colliding with the air causing it to flow, the rotation and shape of the blades cause a pressure differential (Bernoulli effect) that causes the air to flow and give it linear kinetic energy. Part of the force acting on the propeller is opposite the direction of the air, but the Bernouli part is (at least partially) counter the rotational moment of the blade. For this reason, the linear force acting on the propeller could be smaller than the force pushing on the sail. You can think of the sail in terms of drag force. In this case, the larger the sail, the larger the drag force at least until you reach the maximum force produced by the air flow. Newton's laws are not violated.
As a mechanical & aeronautics engineer I can tell you that you're mostly wrong.
By your logic, the air behind the sail is moving faster, so it would have lower pressure (the air in front of the sail is not moving at the start) so it would push the sail backwards. But it obviously doesn't.
Also it doesn't matter how the fan is pushing the air forward. It doesn't matter if it has a horizontal propeller or if it's a different kind of pump style.
Study the free body diagram.
note: the wheels on a surface will have more resistance than a boat on water.
Contrary to Mythbuster’s contention, the operative principles involved here are not “thrust” nor Newton's third law-“For every action, there is an equal and opposite reaction”. Anyone with a basic knowledge of aerodynamics, such as airplane pilots or those who’ve read a book on basic sailing theory, understands that the force causing the boat to move forward or backward is “lift” resulting from a low pressure area. Granted, the momentum of air striking an airfoil, such as a sail, has some “thrust” effect upon the airfoil; however, the “thrust” is negligible compared to the lift resulting from low pressure on the lee side of the airfoil (sail) or propeller.
It is Bernoulli's principle which is operative here. Bernoulli's equations provide that within a horizontal flow of fluid (such as air), where the fluid has a higher speed there will be less pressure than where the fluid is moving at a slower speed.
If you view the Mythbuster’s experiment from the perspective of air speed and consequent low pressure areas, rather than the 'thrust' of air molecules, then you can see why the boat moves in the directions it does.
When the aggregate of the low pressure areas on the lee side of the sail is greater than the aggregate of the low pressure areas on the upwind side of the propeller, the lower pressure on the lee side sail will pull the boat forward.
Conversely, when the propeller is oriented in such a way that the air doesn’t flow sufficiently quickly around the sail (insufficient low pressure), then there is not enough “lift” to pull the boat forward. On the other hand, when the boat moves backwards away from the sail, this is caused by the propeller’s lift being greater than the sail's lift, acting like an airplane’s propeller. In other words, the sail and propeller are in a tug of war, with the greater (cumulative) low pressure lift vectors being the 'pull' that determines which direction the boat moves.
I’ve never had a physics course or studied math beyond the 10th grade of high school (which I flunked twice before passing), so I’m sure an aerodynamics engineer could explain the operative principles here more precisely. Nevertheless, it seems to this layman, the application of Newton’s third law (equal & opposite) and “thrust” is largely irrelevant here.
Bernoulli's Principle is derived from applications of Newton's third law. Newton was slightly prior to Daniel Bernoulli, and the latter studied Newton's works.
Bernoulli's Principle just describes a particular situation of a Newton's third law application.
Furthermore, even if you study Archimedes principle, which is far prior to Isaac Newton, it is still just an application of the third and the second Newton laws.
Newton's law is far more general. If you know the masses and the forces, it might be applied to any situation in any scale short from quantum dynamics, so it is never irrelevant.
As a mechanical & aeronautics engineer I can tell you that you're mostly wrong.
By your logic, the air behind the sail is moving faster, so it would have lower pressure (the air in front of the sail is not moving at the start) so it would push the sail backwards. But it obviously doesn't.