Answer:
gravitational force
electrostatic force
Explanation:
The forces that balloons may exert on each other can be gravitational pull due to the mass of the balloon membrane and the mass of the gas contained in each. This force is inversely proportional to the square of the radial distance between their center of masses.
The Mutual force of gravitational pull that they exert on each other can be given as:

where:
gravitational constant 
are the masses of individual balloons
the radial distance between the center of masses of the balloons.
But when there are charges on the balloons, the electrostatic force comes into act which is governed by Coulomb's law.
Given as:

where:

are the charges on the individual balloons
R = radial distance between the charges.
Answer:
<h2>5.3N</h2>
Explanation:
Step one:
given data
mass of bullfrog= 0.54kg
Step two:
Required
The force F in Newton
From newton first law
F=mg
The acceleration due to gravity acting on the frog is 9.81m/s^2
hence
F=0.54*9.81
F=5.3N
The normal force is 5.3N
Answer:
Concave lenses are used in eyeglasses that correct myopia or nearsightedness.