So they would not slip from your hand if they are refrigerated.
[Added} Depending perhaps on the bottle's design it may also be to make the walls more rigid without needing to increase the thickness of the wall. A similar principle is used on food cans, by rolling a band of corrugations around them.
The indentation strengthens the bottle.
To effectively repair a wall dent, you can start by cleaning the area and filling the dent with spackling compound. Smooth out the surface with a putty knife and let it dry. Sand the area to make it even, then paint over it to match the wall.
It's called a 'punt'.
they are made from plastic because plastic doent dent and is light weight
A concave mark is called a "dent" or "depression." It refers to an indentation or hollow area in a surface.
A dent is a slight hollow in a hard, even surface made by a blow or by the exertion of pressure.
The dent, also known as a punt, in the bottom of bottles is there to increase stability and strength. It helps prevent the bottle from collapsing under the pressure of the liquid inside and also adds a bit of elegance to the bottle's appearance.
To fix a dent in a wiffle ball, you can try gently heating the area with warm water or a hairdryer on low heat to soften the plastic. Once it's warm, carefully press the dent from the inside out with your fingers or a small object to reshape it. After reshaping, allow the ball to cool and harden back into its original form. If the dent persists, replacing the ball may be the best option.
the dent obviously makes the surface not smooth, therefore if the ball hits that spot it won't go off in the right direction, depending on how big the dent is.
Some companies offer a paintless dent removal srvice which is priced by size of dent and location. other than that get behind the dent with a small flat object wood or metal and hammer the block to get rid of the dent. If dent is small use a picking hammer and with the point work around the circle of the dent with the point trying to keep it even with the outside surface. Sand the surface when you get close and go to the flat side of a body hammer and smooth the outside where it got picked out, Apply a small amount fo body filler and sand to even the suface prime sand prime sand with different grits and repaint the surface
To effectively repair a drywall dent, you can start by cleaning the area, filling the dent with spackle or joint compound, smoothing it out with a putty knife, letting it dry, sanding the area, and then painting over it to match the surrounding wall.
To fix a dent in the wall, you can follow these steps: Clean the area around the dent with a damp cloth. Use a putty knife to apply spackling compound to fill in the dent. Smooth out the spackling compound with the putty knife. Let the compound dry completely. Sand the area to make it smooth. Paint over the repaired area to match the rest of the wall.