I have often encounted, in oceanography texts, or in the literature, statements along the lines that the ‘net’ movement of water during the passage of a deep water wave is virtually zero. The key term being ‘net’.
Or, as Artz stated, “relatively” motionless - implying, I assume, that no water is actually displaced, it is lifted then returns to its place. But what Artz is overlooking is that when the wave breaks, then water begins to really move - and how!
I’m just saying that it is silly to say that gravity propels. It is the force that provides objects with mass weight, it doesn’t propel anything, it is always working on all objects with mass.
And those objects with mass slide because of there mass when placed on slippery or low friction/drag slopes, because of the constant force/acceleration of gravity.
If you stand in waist deep water and a wave passes by you it will push you slightly in the direction it’s heading. If you are close to the shore it will push you will a lot of force. Go stand in the water at Sandy Beach or the Wedge and you will see how that works. There’s a lot of energy surging back and forth as the waves move in and the water recedes back. As kids here we learn all about that by playing in the shorebreak. I taught my kids about the ocean’s power this way.
I believe there’s a pushing force just below the water line and surfboards are using that force when turning in the wave face. It’s not all gravity and falling. The pushing force of an unbroken wave (swell) out at sea is different from a wave that has broken. We all know that, that’s why you don’t sit inside of the breaking waves. A trick to catching waves at some spots is to get it after it breaks and let it catch you, then get down below the white water and turn out to get in front. When it’s really big it can break a mile out at some spots and the wave can break 3 times before it hits the inner reef. You can catch the whitewater and work your way into the next breaking section where the wave doubles up and get a geat ride. Sometimes you can ride through 2 doubles and go hundreds of yards.
Skateboards and surfboards can generate speed from turning. You just need to know how to manipulate your board to do it. I don’t know enough about Skiing or snowboarding to say whether that occurs, or if they are just buring off speed. I’ve only used the skis to control decent.
Yes when it breaks there is movement yet it still not the water moving per say. rather the energy pushing the water up and when the water hits a critial point it then moves. You are still dealing with energy forcing the water upward as it passes over a shallow object.
Not intending to be snide, but displacing the water moves it up and down.
And the work was done (by overcoming gravity) placing the object at the top of the slope. The object was propelled to the top fo the slope. My argument is that you wouldn’t say the object was propelled down the slope… it fell down the slope.
I guess it is just semantics, but I just find the gravity discussion moot, because it is always there.
It takes energy to move any object.
The water is moving… that is a FACT.
The moving water is still the medium which allows us to tap into that energy
Yes. The energy is the upward motion – in the opposite direction of gravitational force – that creates a slope.
Ideally, you want to ride the secion of the wave that is not falling – unbroken and steep enough to slide down.
There’s a rush from moving along the ocean even if you are in the broken part of the wave. That’s why so many people get hooked.
Ideally everyone should be riding the part that has already broken going straight in. Only fools want to be riding the part of the wave that’s next to the breaking section. That’s where you get hurt. I’m a fool and I get hurt often.
Pulled, fell…
Agreed.
A bigger rush?
The water also moves shoreward
When it falls forward.
It’s interesting / ironic to me that there can be so much disagreement over such a basic question: what makes surfboards go?
Watch the yellow dots. The water moves slightly forward at the top but then returns to its original position by moving backward.
When it breaks, water falls forward without returning.
The Unbroken Wave
The water waveform has no mass. Only the waveform itself travels toward the shore. I believe the wave does not break if the water is deeper than the wavelength.
Wave animation link:
Stone burner if gravity is the only force how do you explain body surfing.
Gravity…
As the wave lifts the surfer and board their combined potential energy is increased. As the surfer and board drop down the face this potential energy is converted to kinetic energy.
PE = mass * g * height
It is both gravity and the wave height.
(I think that counts as a proof?)