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:
When light travels from one medium to another, the frequency of light does not change. However, the velocity and wavelength change.
Explanation:
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Objects can have the same mass (but different <span>compositions). Only mass or volume cannot tell you if the object is solid or vo</span>lumes) or same volume (but different masses)
Explanation:
8 m × (1000 mm / m) = 8000 mm