3.4 Projectile Motion

The negatives of the components are the components.

The method of addition is the same as the method of subtraction.

You can learn how to add vectors.

Drag onto a graph and change the angle and length.
The magnitude, angle, and components can be seen in a variety of formats.

The motion of falling objects is a type of projectile motion in which there is no horizontal movement.

Motions along the axes are independent and can be analyzed separately.

The motion of the vertical and horizontal were seen to be independent.
The key to analyzing two-dimensional projectile motion is to break it into two motions, one along the horizontal axis and the other along the vertical.
The horizontal axis is called the x- axis and the vertical axis is called the y- axis.
The magnitudes are s, x, and y.

If we kept this format, we would call it displacement with components.

To describe motion, we have to deal with velocity and acceleration and displacement.

The components must be found along the x- and y-axes.
We will assume there are no forces other than gravity.
The components of acceleration are very easy to understand.
Because gravity is vertical.
The equations can be used if both accelerations are constant.

There are components along the horizontal and vertical axes.

It makes an angle with the horizontal.

Break the motion into horizontal and vertical components along the x- and y-axes.

The axes are used.
The initial values are marked with a subscript 0.

The motion can be treated as two separate one-dimensional motions, one horizontal and the other vertical.

The only variable between the motions is time.

To find the total displacement and velocity, combine the two motions.

As the object falls towards the Earth again, the vertical velocity increases in magnitude but points in the opposite direction to the initial vertical velocity.

As the shell reaches its highest point above the ground, the fuse is timed to ignite.

The analysis method outlined above can be used because air resistance is very low for the unexploded shell.

We can define and solve for the desired quantities.

The height is the altitude or vertical position above the starting point.

The apex is the highest point in any trajectory.

The highest point in the trajectory of the shell is found to be at a height of 233 m and 125 m away from the ground.

The component of the initial velocity is in the y-direction.

The initial angle is given by and the initial velocity is given by.

The initial velocity is positive, as is the maximum height, but the acceleration due to gravity is negative.

The maximum height is dependent on the vertical component of the initial velocity, so that any projectile with a 68.6 m/s initial vertical component of velocity will reach a maximum height of 233 m.

The numbers are reasonable for large fireworks displays, the shells of which do reach such heights before exploding.

Air resistance is not completely negligible, and so the initial velocity would have to be larger than given to reach the same height.

There are more than one way to solve the physics problem of time to the highest point.

The easiest method is to use.

The final vertical velocity is zero at the highest point.

This is a good time for large fireworks.

You will notice a few seconds before the shell explodes when you see the fireworks launch.

The horizontal velocity is constant because air resistance is negligible.

In the absence of air resistance, the horizontal motion is constant.

The fireworks fragments could fall on spectators if the horizontal displacement is not used.
Air resistance has a big effect on the shell exploding.

The expression we found for is valid for any projectile motion where air resistance is not very high.

The maximum height of a projectile depends on the vertical component of the initial velocity.

When analyzing projectile motion, it is important to set up a coordinate system.

An origin for the and positions is a part of the coordinate system.

Positive and negative directions are defined in the directions.

The positive vertical direction is usually the direction of the object's motion, while the positive horizontal direction is usually the opposite.

Since it is directed downwards towards the Earth, the vertical acceleration takes a negative value.
Sometimes it's useful to define the coordinates differently.
If you are analyzing the motion of a ball thrown from the top of a cliff, it would make sense to define the positive direction downwards since the motion of the ball is solely in the downward direction.
Take a positive value if this is the case.

The world's most active volcano is in Hawaii.

Red-hot rocks and lava are ejected from active volcanoes.
The rock strikes the side of the volcano at a lower altitude.

The rock was ejected from the volcano.

We can solve for the desired quantities if we resolve this two-dimensional motion into two independent one-dimensional motions.

The time a projectile is in the air is determined by its vertical motion alone.
The rock is rising and falling at the same time.
The final velocity is asked for in this example.
In the first part of the example, the vertical and horizontal results will be recombined to get the final result.

While the rock is in the air, it rises and falls to a final position that is 20.0 m lower than its starting altitude.

We discard the negative value of time because it means an event before the start of motion.

The time for projectile motion is determined by the vertical motion.

Any projectile that has an initial vertical velocity of 14.3 m/s and lands 20.0 m below its starting altitude will spend 3.86 s in the air.

We can find the final horizontal and vertical velocities from the information we have now, combined with the angle it makes with the horizontal.

It's constant so we can solve it at any horizontal location.
Since we know the initial angle and initial velocity, we chose the starting point.

The negative angle shows that the velocity is below the horizontal.

The final altitude is 20.0 m lower than the initial altitude, which is consistent with the fact that the final vertical velocity is negative and therefore downward.

projectile motion shows that vertical and horizontal motions are independent of each other.

The first person to fully comprehend this characteristic was Galileo.
It was used to predict the range of a projectile.
Galileo was interested in the range of projectiles for military purposes.
The range of projectiles can shed light on other interesting phenomena.
We should consider projectile range further.

The maximum range is obtained for a fixed initial speed.

This is not true for other conditions.
The maximum angle is about.
There are two angles that give the same range for every initial angle.
The range depends on the value of gravity.
Alan Shepherd was able to drive a golf ball a long way on the Moon because of the weaker gravity there.

The proof of this equation is left as an end-of chapter problem, but it does fit the major features of projectile range as described.

We assume that the range of a projectile on level ground is very small compared to the size of the Earth.

If the range is large, the Earth will curve away below the projectile and the direction of gravity will change.
The range is larger than predicted because the projectile has more time to fall than on level ground.
If the initial speed is good, the projectile goes into the sky.
It was not possible before centuries.
The Earth curves away from the object at the same rate as it falls.
The object does not hit the surface.
The rotation of the Earth and other aspects of orbital motion will be covered in greater depth later in the text.

We see that thinking about the range of a projectile can lead to other topics, such as the Earth's position.

In addition to velocities, we will look at the addition of velocities, which is an important aspect of two-dimensional kinematics and will yield insights beyond the immediate topic.