Projectile Motion Reflection

     In this week's lab, I learned about projectile motion: how it works and how to analyze it. A projectile is an object in which only the force of gravity is acting upon it. Its general path of motion is a parabolic trajectory.

      Using the Video Physics App on our Ipads, we analyzed the path of motion of a basketball when shot in the air. After taking the video, we plotted points along the ball's path through the air. We then used these points to graph the x and y components of the ball's path.

X-Component

      The top graph shows the x position over time. The change in position over the change in time is also known as the slope. The slope is constant in this case. The bottom graph shows the x velocity over time. Because acceleration is the change in velocity over the change in time and we know that the velocity is also constant, there is no acceleration and no net force.

Y-Component

       The top graph shows the y position over time. The change in position over the change in time is the slope and velocity. The graph shows that the slope is not constant; therefore, the object is accelerating. The bottom graph shows the y velocity over time. The decreasing line crosses the x-axis, and at that moment the object has a velocity of 0, which means it is at its peak. The rest of the time it is decreasing.

Forces in 2D and Circular Motion

Big Questions

1. What does it mean to analyze forces in 2D?

          Analyzing forces in 2D means that there are two dimensions that need to be measured, an x-component and a y-component, which make up a force at a certain angle. Once we break the two dimensions up, we can use SOH CAH TOA to find the magnitude of Fx and Fy. Then we can find Fnetx and Fnety to calculate the total force. The photo shows an example:

2. How do forces cause objects to move in a circle?

          Centripetal force is a center-pointing force that causes objects to move in a circle. The force and velocity act perpendicular to each other. The object does accelerate; however, it is not the magnitude that changes, but the direction. The magnitude remains at a constant speed, but the direction keeps changing. Without this centripetal force, an object would continue to move in a straight line, tangent to the circle. In the hover disk lab we did this week, we spun the disk connected to a rope in a circle at a constant speed. When we let go, the disk continued moving, but in a straight line since there was no centripetal force.

3. What does it mean to be an orbit? How do satellites orbit planets? How do planets orbit the sun?

          In the hover disk lab, the disk orbits the person, just as satellites orbit planets and planets orbit the sun. When something is in orbit, it is constantly moving around another object in a circle. When satellites orbit planets, the centripetal force acting on them is gravity, pulling them to the center. A satellite in space is actually moving at a free-fall toward the planet. The satellite moves in a sideways direction and falls into orbit. The planets orbit the sun in the same way.