Magnus Effect and Table
Tennis
As you might know there are a plethora of spins associated with Table Tennis. There's Top spin, Horizontal spins, Back spin, angled spin, and some more complicated ones. The underlying motion that all spins follow is due to the Magnus Effect, no matter the direction. As stated previously, the top spin hit sends the ball downwards into the table and propels forwards upon hitting it. As was stated in the Magnus Force video I linked on the previous page, the Magnus Force is a force that is perpendicular to the rotational axis.
To the right is an example of top and back spin. They both have the same rotational axis and direction of movement. But the directions of rotation are opposite. The topspin ball sends the air in front of it down under the ball while the backspin ball sends it over the ball. On the topspin diagram the bottom portion of the ball is moving more slowly through the air than the top of the ball (opposite for the backspin diagram). This is due to the velocity of the ball combined with the angular velocities of the top and bottom of the ball which are in opposite directions. The air that is in front of the topspin ball will try Photo Credit : http://www.sciencekids.co.nz
to stick to the ball and will be sent up the back side of the ball until it is forced off of it and sent in a line tangent to the ball at that point.
The picture shown to the left displays the air
movement and
direction of motion for a backspin
ball. As shown in the picture the
air moves tangential to a point on
top of the ball where the air cannot stick
to it any longer. While a majority
of the air is sent off the top of
the ball in a line, a small gap forms
between the two
streams of air flow, this is called a
"deflected wake" which is present when a ball is thrown without spin but is not as deformed as it is when there is spin present. Looking at the backspin picture above, the Magnus Force "Is a Force Photo Credit : https://i.ytimg.com/ perpendicular to the rotational axis" and according to Newton's third law is an equal and opposite force to the deflected air flow. Therefore the force is an upwards force in this case and would be a downwards force for the topspin ball. This is what causes the ball to "dive" down into the table or seem to "float" above the table.
As you might know there are a plethora of spins associated with Table Tennis. There's Top spin, Horizontal spins, Back spin, angled spin, and some more complicated ones. The underlying motion that all spins follow is due to the Magnus Effect, no matter the direction. As stated previously, the top spin hit sends the ball downwards into the table and propels forwards upon hitting it. As was stated in the Magnus Force video I linked on the previous page, the Magnus Force is a force that is perpendicular to the rotational axis.
To the right is an example of top and back spin. They both have the same rotational axis and direction of movement. But the directions of rotation are opposite. The topspin ball sends the air in front of it down under the ball while the backspin ball sends it over the ball. On the topspin diagram the bottom portion of the ball is moving more slowly through the air than the top of the ball (opposite for the backspin diagram). This is due to the velocity of the ball combined with the angular velocities of the top and bottom of the ball which are in opposite directions. The air that is in front of the topspin ball will try Photo Credit : http://www.sciencekids.co.nz
to stick to the ball and will be sent up the back side of the ball until it is forced off of it and sent in a line tangent to the ball at that point.
The picture shown to the left displays the air
movement and
direction of motion for a backspin
ball. As shown in the picture the
air moves tangential to a point on
top of the ball where the air cannot stick
to it any longer. While a majority
of the air is sent off the top of
the ball in a line, a small gap forms
between the two
streams of air flow, this is called a "deflected wake" which is present when a ball is thrown without spin but is not as deformed as it is when there is spin present. Looking at the backspin picture above, the Magnus Force "Is a Force Photo Credit : https://i.ytimg.com/ perpendicular to the rotational axis" and according to Newton's third law is an equal and opposite force to the deflected air flow. Therefore the force is an upwards force in this case and would be a downwards force for the topspin ball. This is what causes the ball to "dive" down into the table or seem to "float" above the table.