No, force does not directly determine velocity; instead, it determines the change in velocity.
Understanding Force and Velocity
The relationship between force and velocity is a fundamental concept in physics, primarily governed by Newton's laws of motion. While often confused, force doesn't set an object's velocity, but rather dictates how that velocity changes.
Newton's First Law and Velocity
According to the first law of motion, an object will maintain its current state of motion unless acted upon by an external force. This means:
- At Rest: A body will remain at rest (velocity of zero) unless a force is applied to it.
- In Motion: If a body is already in motion, it will continue to move at a constant velocity (both speed and direction remain unchanged) unless a force is applied.
As stated in the reference, "velocity is always constant in this law. At rest, velocity remains zero. While in motion, velocity remains the same until a force is applied." This clearly indicates that velocity can exist and persist without a continuous force determining its value. Force is required to alter it.
How Force Influences Velocity: Acceleration
The direct effect of force is on an object's acceleration. Acceleration is the rate at which an object's velocity changes over time. This relationship is described by Newton's Second Law of Motion (though not explicitly detailed in the provided reference, it's the natural progression of the concept):
- Force causes acceleration: When a net force acts on an object, it causes the object to accelerate.
- Acceleration changes velocity: This acceleration then results in a change in the object's velocity (either its speed, its direction, or both).
Therefore, if there is no net force acting on an object, its velocity will remain constant. If there is a net force, its velocity will change.
Key Differences: Force vs. Velocity
To clarify the distinction, consider the following table:
| Feature | Force | Velocity |
|---|---|---|
| Nature | An influence that can cause an object to accelerate. | The rate of change of an object's position. |
| Unit | Newtons (N) | Meters per second (m/s) |
| Effect | Causes a change in velocity (acceleration). | Describes an object's current motion. |
| Need | Required to alter an existing velocity. | Can be constant without a net force. |
Practical Examples
Let's look at a few scenarios to illustrate this concept:
- A Car Cruising on a Highway:
- If a car is moving at a steady 60 mph on a straight road, and assuming negligible air resistance and friction, there is no net force acting on it in the direction of motion. Its velocity remains constant. The engine's force is balanced by opposing forces like air resistance.
- Pushing a Stationary Box:
- When you apply a force to a stationary box, you cause it to accelerate from rest. Its velocity changes from zero to a non-zero value.
- A Ball Thrown Upward:
- Once a ball leaves your hand, the primary force acting on it (ignoring air resistance) is gravity. This downward force causes the ball's upward velocity to decrease, eventually becoming zero at its peak, and then causes a downward velocity to increase. The force of gravity is continuously changing the ball's velocity.
In conclusion, while force is essential for initiating or altering an object's velocity, it does not continuously determine the velocity itself. An object can possess and maintain velocity without an ongoing force.
