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The Physics of Rowing

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on 9 December 2013

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Transcript of The Physics of Rowing

The Physics of Rowing
Terms
Oar: a pole with a flat [almost flat] blade, pivoting in an oar lock, used to row or steer a boat through the water.
Oarlock: A device, usually a U-shaped metal hoop on a swivel in the gunwale, used to hold an oar in place and as a fulcrum in rowing.
Racing Shell: Another name for the boats used for competitive rowing.
Sides: Sculling: 2 oars [1 per hand and on both sides of shell], and Sweeper: 1 oar [port side or starboard]
Coxswain: oar-less crew member who helps steer the boat and lets you know your rating, and time. [either sits in stern or lays in the bow]
Cox Box: A cox box is an electronic device used in competitive rowing that combines a digital stroke rate monitor and elapsed time readout with a voice amplifier.
Ergometer [erg]: rowing machine
Boat Classes:
Junior: Age 19 and under
Senior: Age 23 and under (older than 19)
Master: Age Over 27 & up
Crew Size: 1, 2, 4, 8 [not counting coxswains)
Outrigger [rigger]: a beam, spar, or framework projecting from or over the side of a ship or boat.
Boats float because of the force that pushes downward due to gravity. This is matched by the upward push due to buoyancy.
Speeds of Different Boat Classes
Does the type of boat have an effect on how fast it moves?
In conclusion, the factors of weight, power, strength, boat class, propulsion, resistance, kinetic energy, Centre of Mass, Speed Variation, Balance, and Erg Speed all go together to ensure the coach that he/she will have the best crew out there. Without these studies the coach would not be able to calculate everything that we need(ed) to know about a rower.
Resistance
Bodies moving in liquids slow down due to resistive forces called drag.
Kinetic Energy
A certain boat speed can be reached whether you move a big mass of water slowly or a small mass of water quickly, but the momentum has to stay the same.
Centre of Mass
A rowing shell is not all one body. It is made up of 3 parts: The crew [70-80%], the coxswain [20-30%], and the oars [0-5%].
Balance
Levers
In physics, there are three classes of levers. They are distinguished by three possible linear arrangements of the Fulcrum, the Load, and the Effort.
Relationship Between Power and Weight
The body can produce Anaerobic Power and Aerobic Power
Power and Weight Ratios
Over short distances on the erg (around 1000m), two similar rowers/crew members should have similar power and weight ratios and should be constant. This is using the Anaerobic Power/Weight ratio.
Relationship Between Weight and Erg Speed
An erg measures power which is related to speed. The power is measured by your pressure too. The power and pressure is measured in Watts.
Relationship Between Weight and Boat Speed
Most of the resistance to a moving boat comes from surface drag which is proportional to the wet surface area and the square of the velocity.
Conclusion
Pictures
Video
Propulsion
A boat move through Newton's 3rd Law of Motion [A body continues in a state of rest or uniform motion unless acted upon by an external Force
The rate of change of momentum is proportional to the Force applied
Every Action has an equal and opposite Reaction].
Parts of the Stroke
Catch:
Pictures
THE END!
When your oar moves one way, your shell/boat goes the other
If you look at the puddles after you take your blade out of the water [at the finish], you can obviously tell that the water was moved.
Before: p=0
After: p = mbvb - mwvw = 0
You get the answer above because the total momentum can't change
Drive:
Finish:
Recovery:
In rowing the main kind of drag is Skin Drag: caused by surface friction [between water/liquid and shell]
Skin Drag can be calculated by using this formula:
R=a.v(2)
[v is squared, not multiplied by 2)
It takes less energy to move a large amount of water slowly than it does a small amount of water quickly.
Washing your blade out can cause your boat to move slower because you aren't getting the full stroke in.
The centre mass is the mass-weighed average of the positions of the 3 parts.
When the crew moves one way, the boat has a force going to other.
Gravity acts as the Centre of Mass.
Whether the boat is stale or not depend on the positions of the metacentre and centre of gravity.
The intersection of vertical lines through the centre of buoyancy at various positions called the metacentre.
Similar Physique: having the same build and physiology but not the same weight or height
The ratio of weights of two people with 'similar physique' will be the cube of the ratio of their heights.
Above are the equations
Over long distances on the erg (around 5000m), the lighter or smaller rower/crew member should have the bigger power/weight ratio. This is using the Aerobic Power/Weight ratio.
Load - Fulcrum - Effort
Fulcrum - Load - Effort
Fulcrum - Effort - Load
The arrows in the picture show the different forces on the oar.
The forces on the pin and the stretchers are equal and opposite to the forces on the oar at the fulcrum and handle respectively.
All rowing shells have essentially the same shape.
An eight is longer, wider, and deeper because it has to hold much more weight and people.
For different boats, replacing the weight of the individual W with the total weight of the crew of N members NW
If you coach wants to measure your power/pressure, they can do a watt test.
Your weight can effect your score. On the next slide, there is a picture of one way you can calculate the predicted speed.
Many studies with many equations have showed that in long distance races (5k/10k),light crews are as fast as heavy crews.
Just because the rowers or the boat weigh more than another does not effect the speed.
Full transcript