What makes something a projectile

The only force acting upon a projectile is gravity! A projectile is any object upon which the only force is gravity,. Projectiles travel with a parabolic trajectory due to the influence of gravity,. There are no horizontal forces acting upon projectiles and thus no horizontal acceleration,. The horizontal velocity of a projectile is constant a never changing in value ,.

There is a vertical acceleration caused by gravity; its value is 9. The vertical velocity of a projectile changes by 9.

The horizontal motion of a projectile is independent of its vertical motion. Consider again the cannonball launched by a cannon from the top of a very high cliff. Yet in actuality, gravity causes the cannonball to accelerate downwards at a rate of 9.

This means that the vertical velocity is changing by 9. If a vector diagram showing the velocity of the cannonball at 1-second intervals of time is used to represent how the x- and y-components of the velocity of the cannonball is changing with time, then x- and y- velocity vectors could be drawn and their magnitudes labeled.

The lengths of the vector arrows are representative of the magnitudes of that quantity. Such a diagram is shown below. The important concept depicted in the above vector diagram is that the horizontal velocity remains constant during the course of the trajectory and the vertical velocity changes by 9.

These same two concepts could be depicted by a table illustrating how the x- and y-component of the velocity vary with time. The numerical information in both the diagram and the table above illustrate identical points - a projectile has a vertical acceleration of 9. This is to say that the vertical velocity changes by 9.

This is indeed consistent with the fact that there is a vertical force acting upon a projectile but no horizontal force.

A vertical force causes a vertical acceleration - in this case, an acceleration of 9. But what if the projectile is launched upward at an angle to the horizontal? How would the horizontal and vertical velocity values change with time? How would the numerical values differ from the previously shown diagram for a horizontally launched projectile? The diagram below reveals the answers to these questions. The diagram depicts an object launched upward with a velocity of For such an initial velocity, the object would initially be moving These values are x- and y- components of the initial velocity and will be discussed in more detail in the next part of this lesson.

Again, the important concept depicted in the above diagram is that the horizontal velocity remains constant during the course of the trajectory and the vertical velocity changes by 9. The numerical information in both the diagram and the table above further illustrate the two key principles of projectile motion - there is a horizontal velocity that is constant and a vertical velocity that changes by 9.

As the projectile rises towards its peak, it is slowing down Finally, the symmetrical nature of the projectile's motion can be seen in the diagram above: the vertical speed one second before reaching its peak is the same as the vertical speed one second after falling from its peak. The vertical speed two seconds before reaching its peak is the same as the vertical speed two seconds after falling from its peak.

These concepts are further illustrated by the diagram below for a non-horizontally launched projectile that lands at the same height as which it is launched. Sanders' Site. What is a Projectile? Projectile Motion and Inertia Many students have difficulty with the concept that the only force acting upon an upward moving projectile is gravity.

Describing Projectiles With Numbers: Horizontal and Vertical Velocity A projectile is any object upon which the only force is gravity, Projectiles travel with a parabolic trajectory due to the influence of gravity, There are no horizontal forces acting upon projectiles and thus no horizontal acceleration, The horizontal velocity of a projectile is constant a never changing in value , There is a vertical acceleration caused by gravity; its value is 9.

Time Horizontal Velocity Vertical Velocity 0 s My Resources. Classroom News. My Homework. Recall from the Unit 2 that Newton's laws stood in direct opposition to the common misconception that a force is required to keep an object in motion. This idea is simply not true! A force is not required to keep an object in motion. A force is only required to maintain an acceleration. And in the case of a projectile that is moving upward, there is a downward force and a downward acceleration.

That is, the object is moving upward and slowing down. To further ponder this concept of the downward force and a downward acceleration for a projectile, consider a cannonball shot horizontally from a very high cliff at a high speed. And suppose for a moment that the gravity switch could be turned off such that the cannonball would travel in the absence of gravity? What would the motion of such a cannonball be like? How could its motion be described?

According to Newton's first law of motion , such a cannonball would continue in motion in a straight line at constant speed. If not acted upon by an unbalanced force, "an object in motion will This is Newton's law of inertia.

Now suppose that the gravity switch is turned on and that the cannonball is projected horizontally from the top of the same cliff. What effect will gravity have upon the motion of the cannonball?

Will gravity affect the cannonball's horizontal motion? Will the cannonball travel a greater or shorter horizontal distance due to the influence of gravity? The answer to both of these questions is "No! Gravity causes a vertical acceleration. The ball will drop vertically below its otherwise straight-line, inertial path. By the end of this section, you will be able to do the following:. The learning objectives in this section will help your students master the following standards:.

In addition, the High School Physics Laboratory Manual addresses content in this section in the lab titled: Motion in Two Dimensions, as well as the following standards:. Projectile motion is the motion of an object thrown projected into the air. After the initial force that launches the object, it only experiences the force of gravity.

The object is called a projectile , and its path is called its trajectory. As an object travels through the air, it encounters a frictional force that slows its motion called air resistance. Air resistance does significantly alter trajectory motion, but due to the difficulty in calculation, it is ignored in introductory physics. Ask students to guess what the motion of a projectile might depend on? Is the initial velocity important? Is the angle important?

How will these things affect its height and the distance it covers? Introduce the concept of air resistance. Review kinematic equations. Figure 5. You can see that the cannonball in free fall falls at the same rate as the cannonball in projectile motion.

Keep in mind that if the cannon launched the ball with any vertical component to the velocity, the vertical displacements would not line up perfectly. Since vertical and horizontal motions are independent, we can analyze them separately, along perpendicular axes.

To do this, we separate projectile motion into the two components of its motion, one along the horizontal axis and the other along the vertical. For notation, d is the total displacement, and x and y are its components along the horizontal and vertical axes.

The magnitudes of these vectors are x and y , as illustrated in Figure 5. As usual, we use velocity, acceleration, and displacement to describe motion.

We must also find the components of these variables along the x - and y -axes. Note that this definition defines the upwards direction as positive. Both accelerations are constant, so we can use the kinematic equations. For review, the kinematic equations from a previous chapter are summarized in Table 5.

Where x is position, x 0 is initial position, v is velocity, v avg is average velocity, t is time and a is acceleration. Demonstrate the path of a projectile by doing a simple demonstration.

Toss a dark beanbag in front of a white board so that students can get a good look at the projectile path. Vary the toss angles, so different paths can be displayed. This demonstration could be extended by using digital photography.

Draw a reference grid on the whiteboard, then toss the bag at different angles while taking a video. Replay this in slow motion to observe and compare the altitudes and trajectories. For problems of projectile motion, it is important to set up a coordinate system. The first step is to choose an initial position for x x and y y. This video presents an example of finding the displacement or range of a projectile launched at an angle.

It also reviews basic trigonometry for finding the sine, cosine and tangent of an angle. During a fireworks display like the one illustrated in Figure 5. The fuse is timed to ignite the shell just as it reaches its highest point above the ground. We can then define x 0 x 0 and y 0 y 0 to be zero and solve for the maximum height. By height we mean the altitude or vertical position y y above the starting point.