Tag Archives: Mechanics

Curveball Science

The Magnus effect allows pitchers to throw curveballs, soccer players to bend kicks around defenders, and golfers to launch drives along near-triangular flight paths. This fun physics phenomenon relies on the difference in relative airspeed at various points on the surface of a round object.

GordonDamGif

Viral video captures the Magnus effect in action, 2015. Credit: YouTube channel How Ridiculous. Full footage: https://www.youtube.com/watch?v=QtP_bh2lMXc.

Picture a ball moving through the air while spinning. For the ball to experience a net force, its axis of rotation must be oriented so that some points on the ball’s surface move in the same direction as its trajectory (let’s name one of these points A) while some move the other way (we’ll call an example of this type B).

MagnusDiagram

At point A, the air dragged along by the ball’s surface and the air farther away rush past each other in opposite directions; at point B, they move in the same direction, although one still moves relative to the other (unless rotational speed and flying speed are perfectly matched). This is a bit like the difference between two cars going in opposite directions on the highway and a car in the fast lane passing one in the slow lane.

Like a boat traveling through water, the ball leaves a wake behind as it cuts through the air. The differences between relative airspeeds around a rotating ball cause its wake to pull to one side, resulting in an asymmetrical imbalance of air pressure. This lopsided push bends the ball’s path as it travels.

MagnusGif

A DIY-friendly demonstration of the Magnus effect. Unlike the basketball, which had a backspin as it fell down the dam, the paper roll’s front edge is spinning along with its trajectory. This results in a backwards arc.

The Magnus force affects cylindrical objects in a similar way. Try this at home with a sheet of paper, rolled up and taped into a cylinder. Allow the paper tube to roll off the edge of an angled surface to give it a uniform spin, and watch its path curve!

Written By: Caela Barry

Candle-Powered Seesaw – It’s Physics

Archimedes famously claimed that, given a lever, he could move the whole world. Why so confident, Archimedes? Levers take advantage of a rotational force called torque. You use this force to make your life easier every time you open a door, paddle a boat, turn a wrench, hit a baseball… the list is endless! Here’s the common thread connecting these mechanisms: if you want to turn something, it helps to apply force as far as possible from the axis of rotation.

LeverOhioMost people know this intuitively (or at least through a lifetime of practice). Where do you grip a wrench as you’re tightening a nut? Probably near the end! Try opening a door by pushing right next to the hinges, and it becomes clear why the doorknob is usually all the way on the opposite edge.

A seesaw — or lever — is just an extension of the same idea. One way to make a heavy load manageable is to put it on the other side of a center of rotation, or fulcrum. Then, the farther away the pusher moves, the easier their job becomes. In other words, it’s much easier to move a seesaw by pushing at one end than near the middle. (Lever diagram courtesy of Ohio University.)

So, using a long handle is one way to make rotating (or lifting) an object easier. Of course, it also helps to increase the pushing force, or to make the target load lighter– mass makes a difference, too!

CandleSeesawGif

The candle seesaw shows the effects of changing the mass at each end of a balanced, rotating system. As the lower candle burns, wax drips off, and the candle becomes lighter. The top candle melts, too, but its wax runs down its sides and quickly cools, so the overall mass of that candle doesn’t change. When the bottom end is light enough, the top end swings down, it begins to lose wax itself, and the process repeats.

Written By: Caela Barry

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We would like to thank you for visiting our blog. AstroCamp is a hands-on physical science program with an emphasis on astronomy and space exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and astronomical happenings. This blog has been created by our staff who have at least a Bachelors Degree in Physics or Astronomy, however it is not uncommon for them to have a Masters Degree or PhD. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science, space and astronomy information. Feel free to leave comments, questions, or share our blog with others. Please visit www.astrocampschool.org for additional information. Happy Reading!

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