力 - 物理を学ぶ

Force - Learn Physics Skip to content Topics Introduction to Force Units of Force Types of Forces Newton’s Laws of Motion Applications of Force Measuring and Calculating Force Glossary Quiz What is Force? Force is defined as an interaction that, when unopposed, will change the motion or shape of an object. Force can cause an object to start moving, stop moving, change direction, or change its shape. Because Force can change the state of motion, it is a fundamental concept in mechanics. Force is a vector quantity, meaning it has both magnitude (size) and direction. Units Of Force Measurement The standard unit of force is the Newton (N), which is defined as the force required to accelerate one kilogram of mass at the rate of one meter per second squared. Other units include pounds and dynes. Back to Topics Types of Forces Forces can be categorized into two main types: Contact Forces, and Non-contact Forces Contact Forces Contact forces occur when two objects are physically touching each other. Examples include frictional force, tension force, and normal force. These forces play a significant role in our daily experiences. Frictional Force Frictional force opposes motion between two surfaces in contact, affecting how objects move on surfaces. Tension Force Tension force is transmitted through a string or rope when it is pulled tight by forces acting from opposite ends. Normal Force Normal force is the support force exerted upon an object that is in contact with a stable surface. Non-contact Forces Non-contact forces act without direct physical contact between objects. Examples include gravitational force, electromagnetic force, and nuclear force. They are essential in understanding many physical interactions. Gravitational Force Gravitational force is the attraction between two masses, such as the Earth and objects near it, influencing their motion. Electromagnetic Force Electromagnetic force acts between charged particles, responsible for electricity, magnetism, and light, playing a crucial role in technology. Nuclear Force Nuclear force is the strong interaction that holds protons and neutrons together in atomic nuclei, vital for the stability of matter. Back to Topics Newton’s Laws of Motion Sir Isaac Newton formulated three fundamental laws that describe the relationship between forces and motion. First Law (Law of Inertia) Second Law (F=ma) Third Law (Action and Reaction) First Law (Law of Inertia) An object at rest will remain at rest, and an object in motion will continue in motion with the same speed and in the same direction unless acted upon by a net external force. This law highlights the concept of inertia. Inertia is the property of an object to resist changes in its state of motion. It explains why objects remain at rest or in motion until acted upon. Read more about Inertia here . Applications of the First Law Newton’s First Law has practical applications in everyday life, such as seatbelt safety and vehicle motion. It demonstrates the importance of external forces in changing motion. Importance in Physics This law is foundational in classical mechanics and provides a basis for understanding motion and forces in physics. Second Law (F=ma) Newton’s Second Law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This law can be expressed by the equation F=ma , where F is force, m is mass, and a is acceleration. Force is the interaction that causes an object to accelerate. It is measured in newtons. Mass is the amount of matter in an object. Acceleration is the rate of change of velocity. This law quantifies how forces affect motion. The equation F=ma summarizes the relationship between force, mass, and acceleration in physics. Applications of the Second Law Newton’s Second Law has practical applications in everyday life, for e.g., Pulling a Suitcase, Pushing a Shopping Cart, and Walking. Third Law (Action and Reaction) According to Newton’s Third Law, for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal force in the opposite direction on the first object. Examples of the Third Law Rocket launching, where the action of gas expulsion produces an upward force. Birds flying, where birds push air downwards with their wings. This results in the force that lifts the bird into the air. Car moving, where the wheels of a car push against the road with a force, and the road pushes back allowing the car to move forward. Swimming, where the swimmer pushes water backwards with arms, and the water pushes back propelling the swimmer forward. Back to Topics Applications of Force Force plays a crucial role in various aspects of life, including everyday activities, engineering, technology, and sports. Understanding force helps us design better structures, vehicles, and athletic techniques. Everyday Examples of Force In Action Everyday examples of force as discussed above, include pushing a shopping cart, pulling a suitcase, or even walking. These examples illustrate how force is a constant presence in our daily lives. Application of Force In Engineering and Technology In engineering, understanding force is essential for designing structures, vehicles, and machinery. Engineers apply principles of force to ensure safety, stability, and functionality. The application of force is essential in machinery design for optimal functionality and performance. Application of Force In Sports In sports, athletes utilize principles of force to enhance performance. Understanding how to apply force effectively leads to better techniques in various sports such as basketball, soccer, and gymnastics. Basketball: Effective force application in basketball enhances shooting, passing, and overall gameplay, leading to improved performance. Soccer: In soccer, understanding force helps with kicking techniques, dribbling, and controlling the ball for better outcomes. Gymnastics: Gymnasts use force to execute flips and routines, where precision and control of force determine success. Back to Topics Measuring and Calculating Force Measuring Force Common tools for measuring force include spring scales, load cells, and force gauges. These instruments provide precise measurements of the forces acting on objects. Spring Scales: Spring scales are simple devices that measure force by the extension of a spring. They are commonly used in various applications for weight measurement. Load Cells: Load cells are advanced sensors that convert force into an electrical signal, allowing for precise weight measurements in various industrial applications. Force Gauges: Force gauges are handheld devices used to measure the amount of force applied to an object. They are essential in testing and quality control processes. Calculating Force Force calculations are widely used in physics to analyze the motion of objects and predict their behavior under various conditions. Calculating force often involves using Newton’s Second Law (F=ma) and other related equations. Understanding how to manipulate these equations is crucial for solving physics problems. When multiple forces act on an object, the net force is the vector sum of all those forces. It determines the object’s overall motion. If the net force is zero, the object remains in its current state of motion (either at rest or moving at a constant velocity). Back to Topics Glossary of Key Terms Recap of the Key Terms in Force Applied Force: A force exerted on an object by a person or another object during direct interaction. Balanced Forces: Forces acting on an object that cancel each other out, resulting in no change in the object’s motion. Contact Force: A force that occurs when two objects are physically touching each other, such as friction or tension. Drag Force: A resistive force acting opposite to the direction of motion when an object moves through a fluid such as air or water. Force: A push or pull acting on an object that can change its motion or shape. Friction: A force that opposes the motion or attempted motion of two surfaces in contact. Gravitational Force: The attractive force between two masses. On Earth, it gives objects weight. Net Force: The total force acting on an object after all individual forces have been combined. Normal Force: The force exerted by a surface that supports the weight of an object resting on it. Spring Force: The force exerted by a stretched or compressed spring that acts to restore the spring to its original length. Tension: The force transmitted through a rope, string, or cable when it is pulled tight by forces acting from opposite ends. Unbalanced Forces: Forces that cause a change in the motion of an object because they do not cancel each other. Weight: The force exerted on an object due to gravity. Quiz Recap the concepts you have learnt. Try to answer the questions. You can find the answer to any question by clicking on the icon. What is force? Force is a push or pull acting on an object that can change its motion or shape. Write the formula for force. The formula for force is (F = ma). What is the SI unit of force? The SI unit of force is the newton (N). What is meant by net force? Net force is the vector sum of all the forces acting on an object. What happens when the net force acting on an object is zero? The object remains at rest or continues moving with constant velocity. What is gravitational force? Gravitational force is the force of attraction between two masses. What is friction? Friction is a force that opposes the motion between two surfaces in contact?. What is normal force? Normal force is the force exerted by a surface perpendicular to an object resting on it. What is tension? Tension is the force transmitted through a rope, string, or cable when it is pulled tight. What are balanced forces? Balanced forces are forces that cancel each other and produce no change in motion.