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Balanced and unbalanced forces - their role in motion
In physics, understanding the concepts of force and momentum helps us understand how objects move. One of the primary tools for doing this is Newton's laws of motion. In this explanation, we'll explore how balanced and unbalanced forces play a key role in determining the motion of an object.
Definition of force
Force is the push or pull on an object that results from that object's interaction with another object. It is a vector quantity, which means it has both magnitude and direction. Forces can cause an object to move, stop moving, change direction, speed up, or slow down.
Force is measured in newtons (N), where 1 newton is the amount of force needed to accelerate a 1-kilogram mass at a speed of 1 meter per square second.
What are balanced forces?
Balanced forces are forces that are equal in size but opposite in direction. When the forces on an object are balanced, they cancel each other out, and there is no change in the motion of the object. In simple terms, balanced forces will not accelerate a stationary object or change the speed or direction of a moving object.
Visual example of balanced forces
In the above example, two forces are acting on an object in opposite directions with magnitudes equal to 50 N. Since they are equal and opposite, they balance each other out, resulting in no net force. Therefore, the object will remain in its current state, either at rest or moving at a constant velocity.
Examples of balanced forces
Example 1: A book on the table
Imagine a book sitting on a table. Gravity pulls the book down, and the table exerts an equal and opposite force upward. These forces are balanced, so the book remains at rest.
Example 2: Tug of war
Imagine two teams in a tug of war. If both teams pull with equal force, the rope will not move to either side, demonstrating balanced force.
What are unbalanced forces?
Unbalanced forces occur when two forces acting on an object are not equal in size. When forces are unbalanced, they cause an object to move, change direction, change speed, or change shape.
Visual example of unbalanced forces
Here, the forces acting on the object are not equal. F 1 is greater than F 2. This results in a net force, which accelerates the object in the direction of F 1.
Examples of unbalanced forces
Example 1: Rocking a chair
When you push a stationary chair, you apply a force greater than any resistive force (such as friction). As a result, the chair moves in the direction of the applied force.
Example 2: A football kick
Kicking a stationary soccer ball exerts a force that overcomes friction and air resistance, sending the ball flying across the field. The direction and speed depend on the force applied.
Newton's first law of motion
Newton's first law of motion, also called the law of inertia, states:
An object at rest stays at rest and an object in motion stays in motion unless acted upon by an unbalanced force.This law means that if no net force acts on an object (if all forces are balanced), then the object will maintain its present state, either remaining at rest or moving at a constant velocity.
Example of Newton's first law
If you slide a hockey puck across the ice, it will continue to slide in a straight line at a constant speed unless friction or some other force stops it.
Newton's second law of motion
Newton's second law of motion can be expressed as:
F = m * aWhere:
Fis the net force applied to the object (in newtons),mis the mass of the object (in kilograms), andais the acceleration of the object (in meters per second squared).
This law describes how the velocity of an object changes when an external force is applied to it. It implies that the acceleration of an object depends directly on the net force applied on the object and inversely on its mass.
Example of Newton's second law
Consider pushing two carts, one empty and the other loaded with bricks, by applying the same amount of force. The empty cart (having less mass) will move faster than the cart loaded with bricks due to its lesser mass.
Newton's third law of motion
Newton's third law states:
For every action, there is an equal and opposite reaction.This means that forces always occur in pairs. When one object exerts a force on another object, the second object exerts an equal and opposite force on the first object. This is why when you jump out of a small boat, it slides backward as you move forward.
Example of Newton's third law
When you sit on a chair, your body exerts a downward force on the chair, and the chair exerts an equal upward force on your body.
Role of air resistance and friction
In real-world scenarios, air resistance and friction are forces that commonly act on moving objects, and often balance or counterbalance other forces.
Friction: Acts opposite to the direction of motion, often slowing down the movement of objects. It can exist in many forms, such as sliding, rolling or static friction.
Air resistance: A type of frictional force that acts against an object moving through the air. Its effect is more noticeable at higher speeds, such as for cyclists or airplanes.
Conclusion
Understanding balanced and unbalanced forces provides a fundamental understanding of day-to-day phenomena and lays the groundwork for deeper exploration into the physics of motion. By applying Newton's laws of motion, we can predict and quantify the behavior of objects under different force conditions.
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