# why do objects fall at the same time This is only the case in a vacuum because there are no air particles, so there is no air resistance; gravity is the
only force acting. You can see it for yourselves with this easy Take one piece of A4 paper and scrunch it up into a ball. Take two pieces of identical A4 paper and scrunch them up together into another ball. Your two paper balls should be of similar size but one twice as heavy as the other. Now drop them from the same height at the same time Б you will see that they hit the ground at the same time! There is still air resistance but its effects are the same for both balls as they are the same size and shape. So itБs like thereБs no air resistance at all! Here are two different ways of explaining this phenomenon. б u Explanation using equations: /u Any object of mass em m /em in a gravitational field (in this case EarthБs) has a strong gravitational force /strong, em F /em, acting on it: em F /em #61; ( em GmM /em ) / em R /em sup 2 /sup where em G /em is the gravitational constant (this number does not change, it is the same throughout the whole universe), em M /em is the mass of the Earth, and em R /em б is the distance between the object and the centre of the Earth. It is this force which causes objects to fall to the ground in the first place. NewtonБs Second Law states that a strong force /strong acting on an object will cause a change in speed, or strong acceleration /strong, em a /em, of the object: em F /em #61; em ma б б б б (Very important equation) /em Therefore, the gravitational force will cause the object to accelerate towards the Earth. To find a formula for this acceleration, we combine the two equations for em F /em above: em ma /em #61; ( em GmM /em ) / em R /em sup 2 /sup Then we can divide through by em m /em to get: em a /em #61; ( em GM /em ) / em R /em sup 2 /sup As we can see, em m /em does strong not /strong appear in this formula, meaning that the acceleration of an object in free-fall strong does not depend on its mass /strong. б u БWordyБ explanation: /u Gravity exerts a greater force on a heavy object than on a light object which is what you would expect. em So why donБt heavy objects fall faster? /em The effect of this greater force on the acceleration of the object is cancelled out by the greater mass of the object. To help us understand this, letБs consider the following analogy. Imagine that you have to pull two boxes across a room; one box is twice as heavy as the other. In order to pull them at the same speed you need to pull the heavier box with twice as much force. Gravity pulling objects to the ground is like you pulling boxes across a room. Gravity needs to exert more force on heavier objects to make them fall as quickly as lighter objects. , it was stated that the acceleration of a free-falling object (on earth) is 9. 8 m/s/s. This value (known as the acceleration of gravity) is the same for all free-falling objects regardless of how long they have been falling, or whether they were initially dropped from rest or thrown up into the air. Yet the questions are often asked doesn t a more massive object accelerate at a greater rate than a less massive object? Wouldn t an elephant free-fall faster than a mouse? This question is a reasonable inquiry that is probably based in part upon personal observations made of falling objects in the physical world. After all, nearly everyone has observed the difference in the rate of fall of a single piece of paper (or similar object) and a textbook. The two objects clearly travel to the ground at different rates - with the more massive book falling faster. The answer to the question (doesn t a more massive object accelerate at a greater rate than a less massive object? ) is absolutely not! That is, absolutely not if we are considering the specific type of falling motion known as free-fall. Free-fall is the motion of objects that move under the sole influence of gravity; free-falling objects do not encounter air resistance. More massive objects will only fall faster if there is an appreciable amount of air resistance present. The actual explanation of why all objects accelerate at the same rate involves the concepts of force and mass. The details will be discussed in. At that time, you will learn that the acceleration of an object is directly proportional to force and inversely proportional to mass. Increasing force tends to increase acceleration while increasing mass tends to decrease acceleration. Thus, the greater force on more massive objects is offset by the inverse influence of greater mass. Subsequently, all objects free fall at the same rate of acceleration, regardless of their mass.

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