If you have a large amount of ki flowing in you...

[SaiyajinPrince]

If you had large amounts of ki energy flowing through you would you be lighter then a feather? Or would you be Super dense?

[TheDevilsCorpse]

Ki is a spiritual force. While it can exert pressure and make things feel heavy, I don't think it actually weighs anything...?

[sekzee]

I believe it can have either effect depending on how you use it.

[SaiyajinPrince]

I believe it can have either effect depending on how you use it.

I Would think that in order to handle all that ki we would need to be stronger then a rock

[Polyphase Avatron]

I don't think it changes your weight at all. To fly, you use it to create a repulsive force off the ground like Gohan explained to Videl.

[sekzee]

I believe it can have either effect depending on how you use it.

I Would think that in order to handle all that ki we would need to be stronger then a rock

Videl had enough ki within her to help her fly the entire time, she just did not know how to properly use it.

[SaiyajinPrince]

I don't think it changes your weight at all. To fly, you use it to create a repulsive force off the ground like Gohan explained to Videl.

If your weight doesan't change you'd have to be super dense to take blows like they do on dragon ball z.

[sekzee]

They use ki to amplify their defense as well as their offense.

Look at what happens to foes that are several times stronger and they are caught off guard by an attack: Piccolo kicking Frieza several yards away, and Kid Trunks doing the same thing to Fat Buu.