Local gravity isn't affecting the player?

LocalScripts will only work in areas that the client has partial control over (PlayerGui, ReplicatedFirst, Backpack, Character).

Also, you probably shouldn't keep the gravity after the player lands. If that isn't your goal, I can add some example code.

To have the gravity wear off after a few seconds:

button.Touched:Connect(function() 
oG = workspace.Gravity
workspace.Gravity = 50
wait(5)
workspace.Gravity = oG
end)

To make a jump pad (this will work on the server):

Blacklisted = {} -- Array for blacklisted humanoids - this is to prevent overdoing the jumppower.
local button = script.Parent
button.Touched:Connect(function(part) 
	if game:GetService("Players"):GetPlayerFromCharacter(part.Parent) then
		pHum = part.Parent.Humanoid
		if not table.find(Blacklisted,pHum) then
			table.insert(Blacklisted,pHum)
			-- Set a variable telling us what property to use
			local PropertyName = "JumpHeight"
			if pHum.UseJumpPower then
				PropertyName = "JumpPower"
			end
			local oJP = pHum[PropertyName]
			pHum[PropertyName] = oJP*4 -- 4x power
			pHum.Jump = true -- Make the player jump
			local pConnection = nil
			pConnection = pHum.Touched:Connect(function(floor)
				if floor ~= button then
					pHum[PropertyName] = oJP -- Return their jumppower to normal
					local ind = table.find(Blacklisted,pHum) -- Find their humanoid in the Blacklisted table
					table.remove(Blacklisted,ind) -- And remove it
					pConnection:Disconnect() -- Then disconnect
				end
			end)
		end
	end
end)