Horizontal and Vertical Motions of a Projectile | Grade 9 Science Quarter 4 Week 1

Summary

In this educational video, students are introduced to the concepts of horizontal and vertical motions of a projectile. The lesson begins with a review of Newton's second law of motion, emphasizing the relationship between net force, mass, and acceleration. The video then delves into uniformly accelerated motion (UAM), using real-world examples such as traffic enforcers and vehicles to illustrate the concept. The role of gravity in causing objects to fall is highlighted, and the constant acceleration due to gravity is explained. The distinction between horizontal and vertical motion components in projectile motion is clarified, with horizontal motion characterized by zero acceleration and constant velocity, while vertical motion is influenced by gravity, resulting in increasing velocity. The video uses the example of a marble rolling on a frictionless table to demonstrate these principles. An example problem is solved step by step, calculating the height of a table from which a marble is thrown and its final velocity before impact. The lesson concludes with a shout out to viewers and a teaser for the next part of the lesson, encouraging engagement and further learning.

Takeaways

• 📚 Newton's second law of motion states that the net force acting on an object is equal to the mass of the object multiplied by its acceleration.
• 🚀 Acceleration is a vector quantity that can change over time due to various factors, but in uniformly accelerated motion (UAM), it remains constant.
• 🚦 Traffic enforcers play a crucial role in maintaining traffic flow and ensuring that speed limits are observed, which is an example of non-uniform acceleration in real life.
• 📈 In UAM, the velocity of an object changes by an equal amount in every equal time period, which is characterized by a constant acceleration.
• 🌐 Gravity is the force that pulls objects towards the Earth, causing them to undergo uniformly accelerated motion when in free fall, with an acceleration of 9.8 m/s².
• 🏫 The motion of a projectile, such as a coin tossed upward, is influenced by gravity, causing it to follow a curved path known as a trajectory.
• 🏐 Sepak takraw players exhibit projectile motion when kicking a ball over a net, with the ball following a parabolic trajectory due to gravity.
• 🧮 For horizontally launched projectiles, there is no horizontal acceleration (air resistance neglected), resulting in a constant horizontal velocity.
• 📏 The vertical motion of a projectile is influenced solely by gravity, leading to a constant acceleration of -9.8 m/s², causing the vertical velocity to increase over time.
• 🎯 In the given example problem, the height of the table from which a marble is thrown is calculated using the formula involving gravity and time, resulting in a height of 1.08 meters.
• 🚀 The final velocity of the marble before it hits the ground is determined by combining the horizontal and vertical velocity components using the Pythagorean theorem, resulting in a velocity of 4.84 m/s.

Q & A

What is the second law of motion?

The second law of motion, also known as the law of acceleration, states that the net force acting on an object is equal to the mass of the object multiplied by its acceleration (F_net = m*a).

What is uniformly accelerated motion (UAM)?

Uniformly accelerated motion (UAM) is a type of motion where the velocity of an object changes by an equal amount in every equal time period. It is characterized by a constant acceleration.

How does a speedometer help in understanding acceleration?

A speedometer indicates the speed of a vehicle and can show changes in speed over time. By observing the speedometer readings, one can infer whether the vehicle is accelerating, decelerating, or moving at a constant speed.

What is the acceleration due to gravity?

The acceleration due to gravity is approximately 9.8 meters per second squared (m/s²) and is the constant acceleration that all objects experience when falling towards the Earth, neglecting air resistance.

How does gravity affect projectile motion?

Gravity affects projectile motion by pulling the object downward, causing it to follow a curved path known as a trajectory. This results in a vertical component of motion that is uniformly accelerated, while the horizontal component remains constant.

What are the two types of projectile motion?

The two types of projectile motion are horizontally launched projectiles and angle launched projectiles. Horizontally launched projectiles have an initial velocity purely in the horizontal direction, while angle launched projectiles have an initial velocity at an angle to the horizontal.

What is the horizontal acceleration of a projectile in motion?

The horizontal acceleration of a projectile in motion is zero, assuming no air resistance, because there is no external force acting in the horizontal direction once the projectile is in flight.

What is the formula used to calculate the height of a projectile when given the horizontal distance and initial velocity?

The formula used to calculate the height (h) of a projectile is h = (1/2) * g * t^2, where g is the acceleration due to gravity (9.8 m/s²) and t is the time of flight. Time can be found using the horizontal distance (dx) and initial velocity (v₀x) with the equation t = dx / v₀x.

How do you find the final velocity of a projectile?

The final velocity (Vr) of a projectile can be found using the Pythagorean theorem, which combines the horizontal (Vfx) and vertical (Vfy) components of the velocity: Vr = √(Vfx² + Vfy²).

What is the significance of the negative sign in the vertical component of the final velocity?

The negative sign in the vertical component of the final velocity (Vfy) indicates the direction of the velocity is downward, which is due to the force of gravity acting on the projectile.

How does the script differentiate between horizontal and vertical components of projectile motion?

The script differentiates between horizontal and vertical components by noting that the horizontal component has a constant velocity (Vx) with zero acceleration due to no external force, while the vertical component has a changing velocity (Vy) due to the constant acceleration of gravity (g) acting on it.