Unbalanced forces directly cause an object's motion to change. This means that if an object is standing still, it will start moving, and if it is already moving, its speed will either increase (speed up) or decrease (slow down). As the provided reference states, when forces are unbalanced, "the objects motion will change making it speed up, accelerate, or slow down, decelerate."
What Are Unbalanced Forces?
Forces are interactions (pushes or pulls) between objects. When multiple forces act on a single object, we look at the combined effect, which is called the net force.
- Balanced Forces: If the forces pushing or pulling an object cancel each other out, the net force is zero. The object's motion does not change.
- Unbalanced Forces: If the forces do not cancel each other out, there is a non-zero net force acting on the object. This net force is what causes a change in motion.
How Unbalanced Forces Alter Speed
The presence of an unbalanced force means the object is undergoing acceleration. Acceleration is not just increasing speed; it is any change in velocity, which includes changing speed or changing direction. Regarding speed specifically:
- An unbalanced force acting in the same direction as an object's current motion will cause it to speed up (positive acceleration).
- An unbalanced force acting in the opposite direction to an object's current motion will cause it to slow down (negative acceleration, also known as deceleration).
Here's a simple way to look at it:
Forces Acting on an Object | Net Force | Effect on Object's Speed |
---|---|---|
Balanced | Zero | Speed remains constant (can be zero, i.e., at rest) |
Unbalanced | Greater than 0 | Speed changes (increases or decreases) |
Practical Examples of Unbalanced Forces Changing Speed
Unbalanced forces are responsible for every time something speeds up or slows down in the real world.
- Cycling Faster: Pushing harder on the pedals applies an unbalanced force that overcomes air resistance and friction, causing the bicycle to speed up.
- Catching a Ball: The force exerted by your hands on a moving ball is an unbalanced force that reduces the ball's speed to zero.
- Launching a Rocket: The thrust from the engines provides a large unbalanced force upwards, causing the rocket to accelerate rapidly off the launchpad.
- A Car Braking: The friction force between the brake pads and the wheels, and between the tires and the road, creates an unbalanced force opposite the car's motion, causing it to decelerate.
In essence, any time an object's speed increases or decreases, it is because one or more unbalanced forces are acting upon it, directly causing the change in motion described by the reference material.