 Pictured below are two balls that have different masses. If they are released at the same time, which one will land first? Click on the drop button to see.

The balls landed at the same time. Why is this?

Gravity is the force that pulls objects toward each other. Newton realized that gravity pulls objects straight down toward the center of Earth. When the only force acting on a falling object is gravity, the object is said to be in free fall. An object in free fall accelerates as it falls because gravity acts as an unbalanced force and causes the object to accelerate.

Newton's second law explains why objects fall to Earth with the same acceleration. Let's look at the example again. Let's find the acceleration of each using the formula, a = F over m F m . (Recall that 1 N is the same as 1 kg • m/s2)  What is acceleration?Interactive popup. Assistance may be required. Check your answer  What is acceleration?Interactive popup. Assistance may be required. Check your answer  As you can see, the two balls have the same acceleration even though their masses are different.