The Force of Gravity - Nerdstudy

Gravity is a terminology that we all colloquially understand, but in this lesson, we'll get our first specific introduction to the idea of the "Force of Gravity." Let's revisit Newton's Laws and think about the Force of Gravity based on the concepts that we learned in physics earlier on in the course! Don't forget to like and subscribe please! And as usual, if you've got any questions, feel free to ask away on the comments section. -- Alright! So, the gravitational force near the Earth’s surface has a special property, which is this: all objects are accelerated at the same rate by the force of gravity. No matter what the mass of an object is, the acceleration toward the Earth is going to be the same. So if we ignore things like air resistance, two objects dropped from the same height will hit the ground at the same time. That seems like common sense, but if you actually think about it, this is quite a remarkable property. It means that, even if one object is much heavier than the other, gravity causes them to accelerate at exactly the same rate! But wait! What if we dropped, for example, a feather and a hammer? Even if we drop them from the same height, in real life, they don’t quite hit the ground at the same time! The feather does take alot longer in reality! And although this IS true, the result of this is not due to the difference in gravity. The real difference here is that the feather encounters air resistance, which opposes the force of gravity. The air slows the feather down and prevents it from hitting the ground at the same time as the hammer. Okay then, what if we removed the air? Would they hit the ground at the same time if there weren’t any air resistance? Actually, people have tried that! In fact, they’ve even done this exact experiment on the Moon! And every time they tried it, on the Earth and on the Moon, they found that if there is no air involved, the feather and the hammer hit the ground at the exact same time. Isn’t that neat? Okay, so we’ve established that near the surface of the Earth - and near the surface of the Moon too! - objects are accelerated at the same rate. The next question we could ask is, what is the acceleration? Well, experiments have settled that question. Scientists have measured the acceleration due to gravity to be approximately 9.81 meters per second squared. And the direction of this acceleration is of course downward, toward the center of the earth. If you’ve watched some of our previous videos, you might have seen this number before, but now we know that this value applies to all objects near the Earth. In fact, this value of 9.81 is so common that physicists often represent it with the lowercase letter ‘g’. So from now on, whenever you see this letter ‘g’, you should remember that it represents the magnitude of the acceleration caused by gravity near the surface of the Earth. Awesome! So now we know that the acceleration of any object due to gravity is the same, no matter how heavy it is. And the acceleration has a magnitude of ‘g’, where ‘g’ is approximately equal to 9.81 meters per second squared. Okay. So we’ve talked quite a bit about the acceleration, but in the beginning didn’t we say that that gravity is a force? Well, that’s quite true. So let’s talk about the properties of the gravitational force near the surface of the Earth. First of all, let’s remind ourselves of Newton’s Second Law. It says that force is equal to mass times acceleration. Looking at this equation, one of the first things that we notice is that the direction of the force must be exactly the same as the direction of the acceleration. So if the direction of the acceleration due to gravity is downward, toward the center of the earth, then the direction of the gravitational force must point the same way. The force exerted by gravity is not the same from object to object. In order to understand that, let’s take a look at Newton’s Second Law again. If the magnitude of the acceleration is ‘g’, then what’s the magnitude of the gravitational force? Well, the equation for Newton’s Second Law suggests that we’d get mass times ‘g’. And what does this tell us? Well, we can see that if the acceleration stays the same, then the force must change if the mass changes. It goes up if the mass increases, and goes down if the mass decreases. So the force of gravity changes, compensating for different masses, in order to ensure that the acceleration stays constant!