Introduction:

If you place a ball on the ground, it remains stationary until you kick it with your foot. Similarly, a book on your desk stays still unless you lift it with your hand. When you leave the book after lifting it, the gravitational force pulls it downward. In each of these cases, the motion of the ball or the book changes due to the influence of a pushing or pulling force. In other words, objects accelerate, decelerate, or change their direction only when subjected to an external force.

Article elements:

1.   Force:

2.   Combining Forces:

3.   Balanced and Unbalanced Forces:

4.   Force and Newton's First Law of Motion:

5.   Friction:

6.   Static Friction:

7.   Dynamic Friction:

8.   Rolling Friction:

9.   Force and acceleration:

10.   Newton's Second Law:

11.   Force Units:

12.   Gravity:

13.   Weight:

14.   Gravity and Mass:

15.   Using Newton's Second Law:

16.   Increasing Speed:

17.   Decreasing Speed:

18.   Calculating Acceleration:

19.   Turning:

20.   Conclusion:

Force:

Force is the influencing factor that acts to change the motion of objects, commonly referred to as force. Forces can be either pushing or pulling. When you throw a golf ball, for example, you apply a force, causing the ball to accelerate away from the club. Forces also change the direction of the ball's motion. After leaving the club, the ball's trajectory bends downward as it returns to the ground due to the gravitational force pulling it and altering its movement. When the ball collides with the ground, the Earth exerts a force that stops it. Forces can act in various ways; for instance, a paper clip can be moved by magnetic force, pulled by Earth's gravity, or pushed by your force when you pick it up. All these examples demonstrate forces that can affect a paper clip.

Combining Forces:

It is possible for more than one force to act on an object. For instance, if you hold a paper clip near a magnet, both your force and the magnetic force influence it, along with the gravitational force. The sum of the influencing forces on an object is called the net force. The net force determines how an object's motion changes when multiple forces act on it. When the motion of an object changes, its velocity, and thus acceleration, also change. If forces act in the same direction, they combine to form the net force. If two forces act in opposite directions, the net force equals the difference between them, with its direction in the direction of the larger force.

Balanced and Unbalanced Forces:

A force may act on an object without causing acceleration if other canceling forces are present. If two or more forces act on an object and cancel each other out, resulting in no change in velocity, these forces are called balanced forces. In this case, the net force is zero. If the net force is not zero, the forces are unbalanced, leading to a change in the object's velocity.

Force and Newton's First Law of Motion:

Newton's first law of motion states that an object remains at rest or in uniform motion unless acted upon by an external force. Contrary to the common misconception that continuous force is needed to sustain motion, Newton's insight explains that a force is required only when there is an unbalanced force acting on an object.

Friction:

Friction is the force responsible for stopping the motion of objects, and it opposes the relative motion between surfaces. Friction prevents nearly all objects from moving indefinitely. Galileo's recognition of friction's role in motion led to a better understanding of the nature of motion. Friction can be static or dynamic, depending on whether the object is stationary or in motion.

Static Friction:

When attempting to move a heavy object, such as a refrigerator, you may notice it initially doesn't budge. If you increase your pushing force, it suddenly starts moving. This initial resistance to motion is due to static friction. Static friction arises from the attraction between atoms on the surfaces in contact, causing them to stick together. To overcome static friction and initiate motion, you must exert a force greater than the static friction force.

Dynamic Friction:

Dynamic friction, or kinetic friction, occurs when a body slides or moves over a surface. It acts in the opposite direction of the object's motion, causing a decrease in velocity. Dynamic friction is related to the roughness of the surfaces in contact, and it requires a continuous force to maintain motion against its resistance.

Rolling Friction:

When driving a bicycle or gliding on a skateboard, your speed decreases due to another type of friction called rolling friction. Rolling friction occurs when a body rolls over a surface. In the case of a bicycle, rolling friction is between the tires and the ground, and it contributes to slowing down the bike. Rolling friction is typically less than dynamic friction between the same surfaces, explaining the ease of pushing a box on wheels compared to sliding it.

Newton's second law of motion

Force and acceleration:

During your shopping trip at malls, you need to exert force to push, stop, or change the direction of the cart. Which is easier: stopping a full cart or an empty one, as illustrated in Figure 7? Acceleration occurs when the body's speed increases, decreases, or changes direction. Newton's second law of motion relates the net force acting on a body to its acceleration and mass. The law states that the acceleration of an object is equal to the net force acting on it divided by its mass, with acceleration in the direction of the net force. The acceleration (m/s^2) is calculated using the equation:

Newton's Second Law:

The second law of Newton states that the acceleration of an object is equal to the net force acting on it divided by its mass, and the acceleration is in the direction of the net force.

Force Units:

Force is measured in a unit called the "Newton." Since mass is measured in kilograms (kg) and acceleration in meters per second squared (m/s^2), 1 Newton is defined as the force required to accelerate a 1 kg mass by 1 m/s^2.

Gravity:

Gravity is a familiar force, pulling objects downward. The force of gravity depends on the masses of the objects and the distance between them. Gravity is responsible for Earth's rotation around the sun and the moon's orbit around Earth.

Weight:

The household scale measures weight when you stand on it. Weight is the force of gravity acting on an object and is calculated using the equation:

Gravity and Mass:

Weight and mass are distinct; weight is a force measured in Newtons, while mass is the amount of matter in an object measured in kilograms. Mass is constant, but weight varies with location due to different gravitational forces.

Using Newton's Second Law:

This law is used to calculate acceleration when both mass and the applied force are known. Acceleration is determined by dividing the change in velocity by the change in time.

Increasing Speed:

When an unbalanced force acts on a moving object in the direction of its motion, the object's speed increases. Figure 8 shows how force affects the sled's direction, leading to acceleration and increased speed.

Decreasing Speed:

If an unbalanced force acts opposite to the direction of motion, the object's speed decreases. Figure 9 demonstrates increased friction between the sled and snow, causing a decrease in speed.

Calculating Acceleration:

Newton's second law is used to calculate acceleration. For example, if you pull a box with a force of 5 Newtons and its mass is 10 kg, the acceleration is calculated as \(a = \frac{F}{m}.\)

Turning:

When the net force acting on a moving object is not in the direction of its velocity, the object follows a curved path instead of moving in a straight line. Figure 10 illustrates the gravitational force pulling a basketball downward, causing a curved trajectory.

Conclusion:

Understanding the elements related to force and motion is crucial for comprehending the nature of the world around us. Force reflects the ability to change motion or shape, and combining forces illustrates how their interaction can result in various effects. Balanced and unbalanced forces play a vital role in understanding the state of motion, and applying force and Newton's first law explains how a body's state changes when a force is applied.

On the other hand, friction, in its various forms (static, kinetic, and rolling), appears as a fundamental hindrance to motion and contributes to determining the interaction between objects. Force and acceleration are directly linked to understanding dynamics and changes in motion. Force units form the basis for measuring the impact of forces.

Gravity emerges as a concept that encompasses everything in the universe, and understanding it enhances our comprehension of the motion of falling objects. Weight, mass, and Newton's three laws are the cornerstones of understanding gravitational effects on objects.

Using Newton's second law opens wide doors for understanding the interactions between forces and resulting effects. Changes in speed and acceleration calculations reflect the extent of force impact and acceleration of objects. Turning sheds light on the effect of forces in changing the direction of motion.

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