Physics, Kinematics (1 of 12) What is Free Fall? An Explanation

Summary

In this educational video, the concept of freefall motion is explored, focusing on one-dimensional vertical motion. The video distinguishes between two scenarios of freefall: dropping an object straight down and projecting an object straight up. It emphasizes the significance of considering gravitational acceleration (9.81 m/s² on Earth) and disregarding air resistance. The tutorial proceeds with a practical example of calculating the time it takes for an iPhone to fall 8.75 meters, illustrating the kinematic equations involved and the importance of consistent sign usage. The video concludes with a call to action for viewers to engage with the content by liking, commenting, and subscribing.

Takeaways

• 📚 Freefall is a type of one-dimensional motion that can be vertical and either involve an object falling straight down or being projected straight up and then falling back down.
• 🌐 In freefall problems, air resistance is typically neglected, simplifying the calculations to focus on the effects of gravity alone.
• 🌍 The acceleration due to gravity near Earth's surface is approximately 9.81 m/s², often rounded to 10 m/s² for simplicity in calculations.
• 📉 Freefall motion is characterized by an initial velocity of 0 m/s when an object is dropped and a final velocity of 0 m/s when an object reaches its peak after being thrown upwards.
• 🔢 The kinematic equations used to solve freefall problems involve variables such as initial velocity, final velocity, change in position, acceleration, and time.
• ⏱️ For an object in freefall, the time it takes to reach the ground from a certain height can be calculated using the kinematic equation \( \Delta y = \frac{1}{2} a t^2 \), where \( \Delta y \) is the change in position, \( a \) is the acceleration due to gravity, and \( t \) is the time.
• 🔄 The motion in freefall is unidirectional (in the y-direction), with no movement in the x-direction, simplifying the problem to a one-dimensional issue.
• 📉 When solving freefall problems, it's crucial to be consistent with the use of signs, where downward is considered the negative direction, and upward is positive.
• 📈 The final velocity of an object thrown upwards is the same as its initial velocity but in the opposite direction due to the symmetry of the motion.
• 🎯 In the provided example, the time it takes for an iPhone to fall 8.75 meters from a window is calculated to be approximately 1.34 seconds, illustrating how to apply the kinematic equations to real-world scenarios.

Q & A

What are the two types of freefall motion discussed in the video?

The two types of freefall motion discussed are when an object falls straight down and when an object is projected straight up and then falls back down.

What is the significance of air resistance in the context of freefall problems?

In freefall problems, air resistance is typically ignored, which is why freefall is often defined as motion with no air resistance affecting the object.

What is the standard acceleration due to gravity on Earth's surface in freefall problems?

The standard acceleration due to gravity on Earth's surface is 9.81 m/s^2, which is often approximated as 10 m/s^2 for simplicity in calculations.

How does the acceleration due to gravity on the Moon compare to that on Earth?

On the Moon, the acceleration due to gravity is about one-sixth of that on Earth, which is approximately 1.61 to 1.62 m/s^2.

What is the initial velocity when an object is dropped in freefall?

The initial velocity of an object when it is dropped in freefall is 0 m/s, as it starts from rest.

What is the final velocity of an object at the peak of its trajectory when thrown straight up?

The final velocity of an object at the peak of its trajectory when thrown straight up is 0 m/s, as it momentarily stops before falling back down.

How does the direction of velocity change when an object thrown straight up falls back down?

When an object thrown straight up falls back down, its velocity direction changes from positive (upward) to negative (downward), but the speed remains the same.

What is the relationship between the time it takes for an object to rise and the time it takes to fall back down in freefall?

In freefall, the time it takes for an object to rise to the peak of its trajectory is equal to the time it takes to fall back down.

What kinematic equation is used to solve for time in freefall problems when the initial velocity is zero?

When the initial velocity is zero, the kinematic equation used to solve for time in freefall problems is Δy = -1/2 * a * t^2, where Δy is the change in position, a is the acceleration due to gravity, and t is the time.

How is the time calculated in the example problem where an iPhone is dropped from a window 8.75 meters above the ground?

In the example, the time it takes for the iPhone to reach the ground is calculated using the rearranged kinematic equation t = √(2 * Δy / a), where Δy is -8.75 meters and a is -9.81 m/s^2, resulting in a time of approximately 1.34 seconds.