Projectile Motion - Projectile Fired Horizontally

Michael Flood
29 Apr 201314:13
EducationalLearning
32 Likes 10 Comments

TLDRThis video delves into the physics of projectile motion, focusing on horizontally launched projectiles. It begins with a classic thought experiment comparing a dropped bullet with one fired horizontally from the same height, hypothesizing they hit the ground simultaneously due to gravity's equal effect. To test this, the presenter conducts an experiment using a steel ball bearing, comparing the time it takes to drop versus shoot horizontally, finding near identical results within 1% difference, supporting the theory. The video then explores projectile motion equations, distinguishing between horizontal range (DX) and vertical height (Dy), and explains that while the horizontal motion remains constant, the vertical motion accelerates due to gravity, affecting the time in the air and the projectile's peak height.

Takeaways
  • 🚀 The video discusses the classic physics concept of projectile motion, focusing on both horizontally fired and angled projectiles.
  • 🔍 The most commonly tested concept is the horizontally fired projectile, which the video starts with.
  • 🎯 An experiment is proposed to test the theory that a bullet dropped and a bullet fired horizontally from the same height will hit the ground at the same time due to gravity's equal effect on both.
  • 🧩 A simplified experiment is conducted using a steel ball bearing instead of bullets, with the aim to test the textbook theory without using live rounds.
  • 📏 The experiment involves dropping a ball bearing from table height and firing it horizontally from a pinball shooter, both filmed with a high-speed camera to compare the time to hit the ground.
  • ⏱ The results of the experiment show that the dropped ball bearing takes 4.02 milliseconds to reach the ground, and the fired one takes 4.10 milliseconds, indicating a less than 1% difference.
  • 📚 The video script includes a brief review of projectile motion equations, highlighting the importance of distinguishing between horizontal and vertical motion.
  • 📈 The script explains that projectile motion involves two independent motions: horizontal at constant velocity and vertical under constant acceleration due to gravity.
  • 📊 The horizontal motion is responsible for the range of the projectile, while the vertical motion controls the time in the air and the vertical height attained.
  • 📚 A drawing is suggested for note-taking, illustrating a ball at a certain height above the ground, fired horizontally with an initial velocity, and the resulting parabolic path.
  • 🔍 The video concludes with a mention of the next video in the series, which will discuss projectiles fired at an angle.
Q & A

  • What is the main concept discussed in the video?

    -The main concept discussed in the video is projectile motion, specifically focusing on the comparison between a projectile fired horizontally and an object dropped straight down from the same height.

  • What is the classic physics thought experiment mentioned in the video?

    -The classic physics thought experiment mentioned is that a bullet dropped and a bullet fired horizontally from the same height will hit the ground at the same time due to the effect of gravity being the same on both.

  • What was the initial approach to test the physics thought experiment?

    -The initial approach was to use a steel ball bearing instead of a real bullet and a pinball shooter to simulate the firing of a projectile horizontally, while dropping another ball bearing from the same height for comparison.

  • What method was used to measure the time it took for the ball bearings to hit the ground?

    -A high-speed camera was used to film the ball bearings' descent and count the number of frames it took for each to reach the ground.

  • What was the result of the initial experiment with the steel ball bearings?

    -The result showed that the ball bearing dropped from table height took 402 milliseconds to reach the ground, while the ball bearing fired horizontally took 410 milliseconds, indicating a less than 1% difference and supporting the myth.

  • What is the significance of the term 'range' in projectile motion?

    -In projectile motion, 'range' refers to the horizontal distance (DX) that the projectile travels before it strikes the ground.

  • How does the horizontal motion of a projectile affect its overall motion?

    -The horizontal motion of a projectile is responsible for its range, as it moves at a constant velocity in the horizontal direction, unaffected by gravity.

  • What controls the time in the air for a projectile?

    -The vertical motion of the projectile, which is affected by gravity, controls the time it spends in the air. The greater the vertical distance fallen, the more time in the air.

  • What is the role of the vertical motion in projectile motion?

    -The vertical motion of a projectile is responsible for the time in the air and the vertical height attained. It is influenced by gravity, causing an acceleration that increases the vertical distance fallen over time.

  • What equations are used to analyze the horizontal and vertical motions of a projectile?

    -For the horizontal motion, the equation VX = DX/T is used, indicating constant velocity. For the vertical motion, the equation Dy = 1/2 GT^2 is used, where G is the acceleration due to gravity, to analyze the effect of gravity on the projectile's vertical distance.

Outlines
00:00
🚀 Projectile Motion Experiment: Horizontal Firing vs. Free Fall

In this segment, the video explores the classic physics concept of projectile motion, specifically focusing on the comparison between a horizontally fired projectile and an object in free fall. The experiment aims to test the theory that both objects, dropped and fired from the same height, will hit the ground simultaneously due to the uniform effect of gravity. The presenter uses a high-speed camera to measure the time it takes for a steel ball bearing to drop from table height and the time it takes for the same ball to travel the same horizontal distance when fired from a pinball shooter. The results show a negligible difference of less than 1%, supporting the myth that both the dropped and fired projectiles reach the ground at nearly the same time.

05:00
📚 Understanding Projectile Motion: Horizontal Firing Analysis

This paragraph delves into the theoretical aspects of projectile motion, particularly when a projectile is fired horizontally. The presenter begins with a visual representation of a ball at a certain height above the ground, fired with a known initial velocity. The motion is broken down into horizontal and vertical components, with horizontal motion being constant velocity and vertical motion being accelerated due to gravity. The presenter uses subscript variables to distinguish between the two directions of motion. The horizontal distance traveled, often referred to as 'range,' and the vertical distance, labeled as 'height,' are both discussed. The video also references a strobe light demonstration by Professor Andrew Davidhazy, which illustrates the parabolic path of a pingpong ball in projectile motion. The key takeaways are that the horizontal motion is at a constant velocity and the vertical motion is accelerating due to gravity.

10:00
📘 Separating Motions in Projectile Motion: Horizontal and Vertical Analysis

The video script continues with a detailed analysis of the two independent motions involved in projectile motion: horizontal and vertical. The horizontal motion is characterized by constant velocity, with the equation VX = DX/T used to analyze it, where VX is the horizontal velocity, DX is the horizontal distance (range), and T is the time. This motion is responsible for determining the range of the projectile. On the other hand, the vertical motion is characterized by constant acceleration due to gravity, and the equation Dy = 1/2 GT^2 is used for analysis, where Dy is the vertical distance, G is the acceleration due to gravity, and T is the time. The initial vertical velocity (VIy) is zero, as the projectile starts with no vertical motion. This vertical motion is responsible for the time the projectile spends in the air and the maximum height it reaches. The video concludes this section by emphasizing the importance of understanding these two separate but simultaneous motions in the study of projectile motion.

Mindmap
Keywords
💡Projectile Motion
Projectile motion is the study of an object's flight through the air when launched with a certain velocity and influenced only by gravity. It is a fundamental concept in physics that involves both horizontal and vertical components of motion. In the video, the theme revolves around understanding projectile motion, particularly the classic thought experiment comparing a horizontally fired projectile with a free-falling object.
💡Horizontally Fired Projectile
A horizontally fired projectile is an object launched with an initial velocity in the horizontal direction and no initial vertical velocity. This concept is central to the video, as it discusses the motion of a projectile fired horizontally and its comparison with an object dropped from the same height, emphasizing that both should hit the ground simultaneously due to the effect of gravity.
💡Gravity
Gravity is the force that attracts two objects with mass towards each other, and in the context of projectile motion, it is the force that causes the object to accelerate downwards. In the video, gravity is highlighted as the reason why both the dropped and fired projectiles hit the ground at the same time, as it affects both objects identically in the absence of air resistance.
💡Initial Velocity
Initial velocity refers to the speed and direction of an object at the moment it is launched or released. In the video, the initial velocity is crucial for determining the horizontal range of the projectile. The script mentions firing a ball horizontally with a known initial velocity, which sets the stage for the projectile's motion.
💡Range
Range, in the context of projectile motion, is the horizontal distance traveled by the projectile from the point of launch until it hits the ground. The script discusses measuring the range by firing a ball bearing horizontally and comparing it to the distance a dropped ball bearing would fall, to validate the projectile motion theory.
💡Vertical Motion
Vertical motion is the upward or downward movement of an object, influenced by gravity. In the video, vertical motion is analyzed separately from horizontal motion. It is responsible for the time the projectile spends in the air and the maximum height it reaches, as demonstrated by the ball bearing experiment.
💡Constant Velocity
Constant velocity implies that an object moves at a steady speed in a straight line. In the video, the horizontal component of the projectile's motion is described as having a constant velocity, meaning the ball bearing moves at the same speed horizontally throughout its flight until it is affected by gravity or other forces.
💡Acceleration
Acceleration is the rate of change of velocity of an object. In the video, the vertical motion of the projectile is described as accelerating due to gravity, which means that the speed of the object increases as it falls towards the ground.
💡Parabolic Path
A parabolic path is the curved trajectory followed by a projectile under the influence of gravity, starting from the point of projection and moving in a U-shaped curve until it lands. The video script describes the projectile's path as parabolic, indicating that it moves both horizontally and vertically simultaneously.
💡High-Speed Camera
A high-speed camera is a device capable of capturing multiple images per second at a much faster rate than the human eye can perceive. In the video, a high-speed camera is used to film the drop and the horizontal firing of the ball bearing to accurately measure the time it takes for each to reach the ground, providing empirical evidence for the projectile motion theory.
💡MythBusters
MythBusters is a popular science television show that aims to test the validity of various myths and urban legends, often using experiments and demonstrations. In the script, the presenter mentions MythBusters in the context of carrying out the bullet experiment, suggesting a connection to the show's approach of testing scientific concepts through practical experiments.
Highlights

The study of projectile motion covers both horizontally fired and angled projectiles, with a focus on the former.

A classic physics thought experiment suggests that a bullet dropped and one fired horizontally from the same height will hit the ground simultaneously due to the uniform effect of gravity.

The experiment's difficulty has meant that it has rarely been tested with real bullets and guns.

A plan is proposed to test the theory using a steel ball bearing and a pinball shooter as a safer alternative to live ammunition.

The ball bearing is dropped from table height and filmed with a high-speed camera to measure the time taken to hit the ground.

The ball bearing is also shot horizontally using the pinball shooter to compare the time taken to reach the floor.

The results show that the dropped ball bearing and the fired one hit the ground with a difference of less than 1%, supporting the myth.

A more traditional gun-based experiment is suggested for further testing, but not performed in the video.

A drawing is used to illustrate the key variables in projectile motion, such as initial velocity, height, and range.

Projectile motion involves two independent motions: horizontal at constant velocity and vertical under constant acceleration due to gravity.

The horizontal motion is responsible for the range of the projectile, while the vertical motion controls the time in the air and the height attained.

A strobe light is used to capture images of a pingpong ball in motion, illustrating the parabolic path of projectile motion.

The vertical motion shows an increasing distance between equal time frames, indicating acceleration due to gravity.

The horizontal motion of the pingpong ball remains constant, indicating no acceleration in the horizontal direction.

The equations for analyzing horizontal motion are simplified due to the lack of acceleration in that direction.

The vertical motion is analyzed using the equation that accounts for initial velocity, time, and acceleration due to gravity.

The video concludes with a summary of the factors influencing the projectile's range, time in the air, and maximum height.

Transcripts

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Projectile MotionPhysics ExperimentHorizontal FiringGravity EffectsMythBustersBall BearingHigh-Speed CameraParabolic PathMotion AnalysisEducational Video