Chapter 1-5 Review: Center of Mass, Kinematics, and Forces

A curated set of questions and answers covering center of mass, velocity/acceleration concepts, constant forces, kinematics at takeoff, drag and lift, and related physics ideas from Chapters 1–5.

What is the center of mass (COM)?

The balance point of a body where its mass is concentrated.

How does moving mass within the body affect the center of mass?

As mass is moved in a direction, the center of mass shifts in that same direction (follows the mass distribution).

If you move a large portion of mass forward and down (e.g., the upper body), what happens to the COM?

The COM moves forward and downward with the mass shift.

What happens to the COM if you abduct your right shoulder (move mass to the right)?

The COM moves upward and to the right in that direction.

To predict where a mass will be a short time in the future, what information do you need?

Its velocity (first derivative of position) and acceleration (second derivative of position).

What does negative velocity indicate on a position versus time graph?

The position is decreasing over time (the slope is downward).

On a position-versus-time graph, what does a moment of zero velocity look like?

A flat (horizontal) section where the slope is zero.

Is acceleration constant during most ground movement?

No. While airborne, gravity provides a relatively constant vertical acceleration; during ground contact, forces vary with time.

When is acceleration effectively constant for a moving person?

When you are airborne and not in contact with the ground, so gravity is the dominant constant force.

What part of the motion can be used with kinematic equations to determine takeoff angle?

The instantaneous launch kinematics at takeoff.

Why might takeoff angle not be the only important factor for maximizing range?

There are other factors that can be more important than the takeoff angle for achieving optimal range.

What are the directions of drag and lift forces relative to motion?

Drag acts opposite to the direction of motion; lift acts perpendicular to the direction of motion.

How is the lift force equation similar to the drag equation, and what terms differ?

Both involve coefficients and area; drag uses drag coefficient (CD) and frontal area, lift uses lift coefficient (CL) and surface/wing area.

What is one way to reduce drag during motion through air?

Ducking down to reduce frontal area and create a smoother flow reduces drag.

At typical running speeds, how significant are drag forces?

Usually negligible; drag becomes more significant at very high speeds or with heavy loads.

What physical effect explains why spiraling a football can increase distance?

Lift generated by spin (Magnus effect) can extend the range of the ball.