To determine the amount of helium needed to lift a 1 kg iron ball off the ground, we need to consider the buoyant force and the weight of both the iron ball and the helium.
The buoyant force exerted on an object submerged in a fluid (in this case, helium) is equal to the weight of the fluid displaced by the object. For an object to float or be lifted off the ground, the buoyant force must be greater than or equal to the weight of the object.
The weight of the iron ball is 1 kg multiplied by the acceleration due to gravity (approximately 9.8 m/s^2), which gives us 9.8 newtons.
To calculate the amount of helium needed, we need to find the weight of the displaced air by the iron ball. Since helium is much lighter than air, we can assume that the weight of the displaced air is approximately equal to the weight of the helium.
The density of helium is about 0.18 kg/m^3, while the density of air is about 1.2 kg/m^3. Therefore, the weight of the displaced air (and the helium) is 1 kg multiplied by the acceleration due to gravity (9.8 m/s^2), which gives us 9.8 newtons.
So, to lift the 1 kg iron ball off the ground, you would need approximately 9.8 grams (0.0098 kg) of helium.