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9.2. Free Fall
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Today we are going to talk about free fall. Can anyone tell me what free fall means?
Is it when something falls without anything holding it up?
Exactly! Free fall refers to the motion of an object when gravity is the only force acting on it. How do you think this might differ from other types of motion?
Maybe because it falls straight down? Other objects might move sideways or upward?
Great observation! In free fall, an object moves downwards due to the pull of gravity, accelerating as it descends. This acceleration is known as 'g', approximately 9.8 m/s² on Earth.\nLet's remember that: 'Free fall means no forces but gravity!'
So, if I drop a heavy rock and a light feather, they'll still fall due to gravity?
Yes! Would you believe they're going to hit the ground at the same time?
I thought heavier things fall faster?
That's a common myth! We'll explore that further through some experiments in a bit. But first, remember the meaning: Free fall is solely about the force of gravity!
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Let’s get into how acceleration works in free fall. Can anyone tell me what acceleration means?
It's when something speeds up?
Exactly! In the case of free fall, the acceleration is caused by the force of gravity, which pulls everything towards the center of the Earth. Can anyone remember what we denote this acceleration as?
Is it g?
That's right! And it has a value of approximately 9.8 m/s². That means for every second an object is falling, its speed increases by about 9.8 m/s. We can remember it with the phrase, 'g is the gravity gain!'\nCan anyone give me an example of this?
A skydiver falling would gain speed until they deploy their parachute?
Spot on! The skydiver experiences free fall until the parachute opens, reducing their speed. By understanding this, we can calculate the distance fallen using our equations of motion.
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Create a free accountLet's conduct an experiment. We'll drop two objects of different weights from the same height. Who wants to help?
I do! What will we drop?
We’ll drop a stone and a piece of paper at the same time. Remember to look closely and see what happens!
I see the stone is falling faster than the paper!
Wait, the paper is wiggling in the air. Isn't that because of air resistance?
Exactly, Student_4! The paper is affected by air resistance, which slows it down. In a vacuum, both the paper and stone would hit the ground simultaneously. So, can someone explain why mass doesn’t affect free fall in a vacuum?
Because gravity pulls equally on all objects regardless of their mass!
Right again! Always remember: in the absence of air resistance, all objects accelerate the same due to gravity.
Overview
Short Summary
This section explains the concept of free fall and the effects of gravity on falling objects.
Medium Summary
In this section, students learn about free fall as the motion of objects under the influence of gravitational force, which leads to acceleration towards the Earth. Various activities demonstrate that all objects fall at the same rate regardless of their mass, and the section also introduces the calculation of gravitational acceleration, denoted as g.
Detailed Summary
Detailed Summary
The concept of free fall refers to the motion of objects falling under the influence of gravity alone, with no other forces acting on them, such as air resistance. When an object is released and falls towards the earth, it accelerates due to the gravitational pull, which is denoted by g and has an approximate value of 9.8 m/s² near the Earth's surface. In this section, activities are provided to visualize the principles of free fall. One notable experiment illustrates that heavy and light objects fall at the same rate, contradicting the common perception of mass influencing fall speed. Students are encouraged to understand how resistance can affect different objects, such as a feather and a stone, emphasizing that mass does not matter when only gravity acts on the object.
Additionally, the section reviews the equations of motion for free-falling objects, allowing students to calculate the distance fallen and final velocities. Understanding these principles prepares students for real-world applications, such as projectiles and understanding gravitational effects in various contexts.
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Audio Book
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Create a free accountLet us try to understand the meaning of free fall by performing this activity.
• Take a stone. • Throw it upwards. • It reaches a certain height and then it starts falling down.
We have learnt that the earth attracts objects towards it. This is due to the gravitational force. Whenever objects fall towards the earth under this force alone, we say that the objects are in free fall.
Detailed Explanation
Free fall refers to the motion of objects when they are falling only under the influence of gravity, with no other forces acting on them, such as air resistance. When you throw a stone upwards, it goes up until gravity stops it and pulls it back down. During this fall, the stone is in free fall because the only force acting on it is the gravitational force from the Earth, making it accelerate towards the ground at a rate of about 9.8 m/s².
Examples & Analogies
Imagine dropping a ball off a building. Initially, it begins to fall faster and faster until it hits the ground. During the entire fall, except for wind resistance, the only thing acting on the ball is the Earth's gravitational pull, making it a perfect example of free fall.
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Create a free accountWhile falling, there is no change in the direction of motion of the objects. But due to the earth's attraction, there will be a change in the magnitude of the velocity. Any change in velocity involves acceleration. Whenever an object falls towards the earth, an acceleration is involved. This acceleration is due to the earth’s gravitational force. Therefore, this acceleration is called the acceleration due to the gravitational force of the earth (or acceleration due to gravity). It is denoted by g, and the unit of g is the same as that of acceleration, that is, m s².
Detailed Explanation
The acceleration due to gravity (g) is the rate at which an object accelerates when it is in free fall. Near the Earth's surface, the value of g is approximately 9.8 m/s². This means that for every second an object is falling, its speed increases by about 9.8 m/s, due to the gravitational pull from the Earth. This acceleration is constant for all objects, regardless of their mass, as long as the height is small enough to ignore air resistance.
Examples & Analogies
If you drop two objects, like a feather and a hammer, in a vacuum where there's no air, they will both hit the ground at the same time, despite the hammer being much heavier. This is because they both experience the same acceleration due to gravity, demonstrating that gravity affects all objects equally.
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Create a free accountTo calculate the value of g, we should put the values of G, M, and R in Eq. (9.9), namely,
g = G M/R²
where G is the universal gravitational constant, M is the mass of the earth, and R is the radius of the earth. Thus, g = 9.8 m/s².
Detailed Explanation
The formula for calculating gravitational acceleration (g) is derived from Newton's law of universal gravitation. In the formula g = G(M/R²), G is a constant value, while M is the Earth's mass, and R is the distance from the center of the Earth to its surface. When you plug in the appropriate values, you find that g is approximately 9.8 m/s², which is the gravitational acceleration experienced by objects near the Earth's surface.
Examples & Analogies
Think about throwing a basketball into the air and watching it fall back down. The constant acceleration of 9.8 m/s² explains how quickly it slows down at the top of its arc and then speeds up as it falls. This formula allows scientists to calculate how fast any object will fall based on its distance from Earth's center.
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Create a free accountLet us do an activity to understand whether all objects hollow or solid, big or small, will fall from a height at the same rate.
• Take a sheet of paper and a stone. • Drop them simultaneously from the first floor of a building. Observe whether both of them reach the ground simultaneously.
Detailed Explanation
This activity illustrates that while all objects fall due to gravity, their motion can be affected by air resistance. In this case, the stone, being denser and more streamlined, will fall faster than the sheet of paper, which flutters and encounters greater air drag. In a vacuum, where there is no air resistance, both objects would fall at the same rate, demonstrating that gravity applies equally to all regardless of mass.
Examples & Analogies
This can be likened to a feather and a bowling ball dropped from the same height. In the absence of air, they would hit the ground at exactly the same time. However, in reality, the feather floats down much slower while the bowling ball plummets straight down quicky due to air resistance acting on the feather.
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Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Free Fall: The motion of falling objects solely influenced by gravity.
Acceleration due to Gravity (g): The rate at which an object accelerates as it falls, approximately 9.8 m/s².
Air Resistance: A force opposing motion through air that affects how quickly objects fall.
Examples
Memory Aids
Interactive tools to help you remember key concepts
Stories
Flash Cards
Glossary
Free Fall
The motion of an object falling under the influence of gravity alone, without any other forces acting on it.
Acceleration
The change in velocity of an object per unit time; in free fall, it is caused by gravitational force.
g
The acceleration due to gravity, approximately 9.8 m/s² near the surface of the Earth.
Air Resistance
The force that opposes the motion of an object through air, affecting how quickly it falls.