Gravity plays a crucial role in our everyday lives, affecting everything from our to how objects fall. Understanding the relationship between and is key to grasping the concept of gravity and its effects on Earth and beyond.
Air resistance and weightlessness are fascinating aspects of gravity's influence. These concepts explain why skydivers reach and why astronauts float in space, showcasing the complex interplay between gravity and other forces in different environments.
Mass, Weight, and Gravity
Mass vs weight relationship
Mass represents the intrinsic property of an object, measuring the amount of matter it contains (atoms, molecules)
Remains constant regardless of location (Earth, Moon, space)
Measured in kilograms (kg) or slugs (imperial units)
Determines an object's , or resistance to changes in motion
Weight is an extrinsic property, the exerted on an object due to gravity
Varies depending on the strength of the gravitational field (Earth vs Moon)
Measured in newtons (N) or pounds (lbs)
Weight is directly proportional to mass, related by the equation [w = mg](https://www.fiveableKeyTerm:w_=_mg)
w represents weight, m represents mass, [g](https://www.fiveableKeyTerm:g) represents
On Earth's surface, g is approximately 9.8 m/s2 or 32 ft/s2
Examples
A person with a mass of 70 kg weighs about 686 N on Earth
The same person would weigh about 114 N on the Moon, where g≈1.62 m/s2
Air resistance effects on falling
motion occurs when an object is under the influence of gravity alone
Acceleration is constant and equal to the (g)
Neglects air resistance for simplicity
Air resistance is a force acting opposite to the direction of motion
Increases with the object's velocity and surface area (parachute vs bullet)
Causes objects to reach a when air resistance equals the force of gravity
Air resistance reduces the acceleration of falling objects
Objects with different masses but similar surface areas fall at similar rates (paper vs coin)
Explains why a feather and a bowling ball fall at different rates in air but at the same rate in a vacuum
Examples
A skydiver reaches a terminal velocity of about 55 m/s (120 mph) due to air resistance
A penny and a feather dropped from the same height in a vacuum will hit the ground simultaneously
Conditions for weightlessness
Weightlessness occurs when an object appears to have no weight
The only force acting on the object is gravity
Conditions that create weightlessness
: Objects experience apparent weightlessness (skydiving, amusement park rides)
Orbit: Spacecraft and astronauts experience continuous free fall around a celestial body (ISS)
Deep space: Far from massive objects, the is negligible
Implications of weightlessness
In free fall and orbit, objects experience apparent weightlessness
Astronauts can float and maneuver easily within a spacecraft
In deep space, the lack of significant gravitational forces presents challenges
Maintaining astronaut health (bone , muscle mass)
Controlling the orientation and trajectory of spacecraft
Examples
An astronaut on the ISS experiences weightlessness due to continuous free fall around Earth
A spacecraft traveling far from any massive objects would experience true weightlessness
Density, Pressure, and Buoyancy
Density is the mass per unit volume of an object or substance
Affects how objects interact with fluids and their
is the force applied per unit area
Relevant in understanding fluid dynamics and atmospheric effects
Buoyancy is the upward force exerted by a fluid on an immersed object
Determines whether an object will float or sink in a fluid
Related to the density of the object compared to the fluid's density
Key Terms to Review (43)
Acceleration due to gravity: Acceleration due to gravity is the rate at which an object accelerates when falling freely towards a massive body, like Earth, due to gravitational pull. On Earth's surface, this value is approximately $9.8 \text{ m/s}^2$.
Acceleration Due to Gravity: Acceleration due to gravity, often denoted as 'g', is the acceleration experienced by an object due to the Earth's gravitational pull. This constant acceleration affects the motion of objects near the Earth's surface, influencing various physical phenomena such as free fall, mass, weight, and gravitational fields.
Acceleration vector: An acceleration vector is a vector quantity that represents the rate of change of velocity of an object. It indicates both the magnitude and direction of this change.
Action-at-a-distance force: An action-at-a-distance force is a force exerted by an object on another object that is not in physical contact with it, acting over a distance through space. Examples include gravitational, electromagnetic, and nuclear forces.
Apparent weight: Apparent weight is the normal force exerted by a surface on an object, which can differ from the object's true weight due to acceleration. It may be perceived differently in scenarios like elevators or free-fall.
Beam Balance: A beam balance is a device used to measure the mass of an object by comparing it to a known standard mass. It consists of a horizontal beam that is supported at its center and has equal-length arms, with pans or platforms attached to each end to hold the objects being weighed.
Buoyancy: Buoyancy is the upward force exerted by a fluid on an object immersed in it, which counteracts the object's weight and allows it to float. This principle is fundamental to understanding the behavior of objects in various contexts, including mass and weight, drag force and terminal speed, and fluids, density, and pressure.
Center of gravity: The center of gravity is the point at which the entire weight of a body or system can be considered to act. It is crucial for analyzing static equilibrium and stability in physical systems.
Center of Gravity: The center of gravity is the point at which an object's weight appears to be concentrated. It is the average location of the weight of an object, where the object would balance if it were suspended from that point.
Center of mass: The center of mass is the point in an object or system where all its mass can be considered to be concentrated for the purpose of analyzing translational motion. It is the weighted average position of all the mass in the system.
Center of Mass: The center of mass is the point at which an object's entire mass can be considered to be concentrated. It is the average position of the mass of an object, and it is the point around which the object's rotation and motion can be analyzed.
Density: Density is a fundamental physical property that describes the mass per unit volume of a substance. It is a measure of how much matter is packed into a given space and is a crucial concept in understanding the behavior of fluids, solids, and gases across various physics topics.
F = ma: The equation F = ma represents Newton's second law of motion, which states that the force acting on an object is equal to the mass of that object multiplied by its acceleration. This fundamental principle connects the concepts of force, mass, and acceleration, illustrating how they interact in physical systems. Understanding this relationship is crucial for solving problems related to motion and dynamics in various contexts.
Force: Force is a vector quantity that represents the interaction between two objects, causing a change in the motion or shape of the objects. It is the fundamental concept that underlies many of the physical principles studied in college physics, including Newton's laws of motion, work, energy, and more.
Free fall: Free fall is the motion of an object under the influence of gravitational force only. It neglects air resistance and assumes a uniform acceleration due to gravity.
Free Fall: Free fall is a state of motion where an object is falling under the sole influence of gravity, without any other external forces acting upon it. This term is closely connected to the topics of motion with constant acceleration, projectile motion, Newton's second law, and gravitational effects near Earth's surface.
G: The acceleration due to gravity, commonly denoted as 'g', is a fundamental physical constant that represents the acceleration experienced by an object in free fall near the Earth's surface. It is a measure of the strength of the Earth's gravitational field and plays a crucial role in the understanding of various physical phenomena, particularly in the context of free fall and the relationship between mass and weight.
Gravitational Constant: The gravitational constant, denoted as 'G', is a fundamental physical constant that describes the strength of the gravitational force between two objects. It is a crucial parameter in understanding the laws of gravitation and the motion of objects under the influence of gravity.
Gravitational Force: Gravitational force is the attractive force that exists between any two objects with mass. It is the force that causes objects to be pulled towards each other, and is the fundamental force responsible for the motion of celestial bodies and the behavior of objects on Earth.
Inertia: Inertia is the property of an object that resists changes to its state of motion. It depends solely on the mass of the object.
Inertia: Inertia is the property of an object that resists changes to its state of motion. It is the tendency of an object to remain at rest or in motion unless acted upon by an unbalanced force.
Isaac Newton: Isaac Newton was an English mathematician, physicist, astronomer, and natural philosopher who is widely regarded as one of the most influential scientists of all time. His groundbreaking work in the fields of classical mechanics, optics, and mathematics laid the foundation for our understanding of the physical world and the laws that govern it.
Kilogram: A kilogram is the base unit of mass in the International System of Units (SI). It is defined by the mass of the International Prototype Kilogram, a platinum-iridium alloy cylinder kept at the International Bureau of Weights and Measures.
Kilogram: The kilogram is the base unit of mass in the International System of Units (SI). It is the only SI unit that is still defined by a physical object, rather than a fundamental physical constant. The kilogram is a crucial concept in physics, as it is used to quantify the amount of matter in an object and is a key component in the study of mechanics, thermodynamics, and other areas of physics.
Law of Gravitation: The law of gravitation, also known as Newton's law of universal gravitation, is a fundamental principle that describes the gravitational force between any two objects in the universe. It states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Linear mass density: Linear mass density is the measure of mass per unit length of a one-dimensional object, such as a string or rod. It is typically denoted by the symbol $\lambda$ and expressed in units of kg/m.
Mass: Mass is a fundamental physical quantity that represents the amount of matter in an object. It is a measure of an object's resistance to changes in its state of motion, and it is a key concept in the study of mechanics and the behavior of objects under the influence of forces.
Newton: Newton is the standard unit of force in the International System of Units (SI), named after the renowned English physicist and mathematician, Sir Isaac Newton. It is a fundamental unit that is essential in understanding and describing the behavior of objects under the influence of various forces, as well as in the study of mechanics, dynamics, and other related areas of physics.
Newton's Laws: Newton's laws are a set of three fundamental principles that describe the relationship between an object and the forces acting upon it, governing the motion of physical bodies. These laws form the foundation of classical mechanics and are essential for understanding and solving problems in physics.
Normal Force: Normal force is the support force exerted by a surface perpendicular to the object resting on it, preventing the object from falling through the surface. It plays a crucial role in balancing other forces acting on an object, particularly in scenarios involving gravity and acceleration.
Pound: A pound is a unit of weight commonly used in the United States and other countries that employ the imperial system. It quantifies the force exerted by gravity on an object’s mass and is often abbreviated as 'lb.' This measurement is crucial in distinguishing between mass, which is a measure of the amount of matter in an object, and weight, which depends on gravitational pull.
Pressure: Pressure is a measure of the force applied per unit area, representing the amount of force exerted on a surface or object. This concept is fundamental in understanding various physical phenomena and principles, including mass and weight, hydraulic systems, fluid dynamics, sound propagation, and shock waves.
Scalar: A scalar is a quantity that has only magnitude and no direction. Common examples include mass, temperature, and time.
Scalar: A scalar is a physical quantity that has only magnitude and no direction. It is a single numerical value that represents the size or amount of something, without any associated directional information.
Slug: A slug is a unit of mass used in the imperial system, specifically defined as the mass that is accelerated by one foot per second squared when a force of one pound is applied. This unit plays a crucial role in distinguishing between mass and weight, especially in contexts involving Newton's laws of motion, where understanding the difference can lead to better comprehension of how objects behave under various forces.
Spring Scale: A spring scale is a type of weighing device that measures the force exerted on it, typically the weight of an object, by using the elastic properties of a spring. It is commonly used to measure the mass or weight of an object in the context of physics and everyday applications.
Terminal velocity: Terminal velocity is the constant speed that a freely falling object eventually reaches when the resistance of the medium prevents further acceleration. It occurs when the drag force equals the gravitational force acting on the object.
Terminal Velocity: Terminal velocity is the maximum speed that an object can reach while falling through a fluid, such as air or water, due to the balance between the downward force of gravity and the upward force of drag. This concept is fundamental in understanding the motion of objects under the influence of gravity and air resistance.
Universal gravitational constant: The universal gravitational constant, denoted as $G$, is a fundamental physical constant that quantifies the strength of the gravitational force between two masses. Its value is approximately $6.674 \times 10^{-11} \text{Nm}^2\text{kg}^{-2}$.
Vector: A vector is a mathematical quantity that has both magnitude (size or length) and direction. It is used to represent physical quantities in physics, such as displacement, velocity, acceleration, and force, where both the size and the direction of the quantity are important.
W = mg: The equation $w = mg$ represents the relationship between the weight (w) of an object, its mass (m), and the acceleration due to gravity (g). This fundamental relationship is a key concept in understanding the physics of mass and weight.
Weight: Weight is the force exerted on an object due to gravity. It is calculated as the product of an object's mass and the acceleration due to gravity.
Weight: Weight is the force exerted on an object due to the pull of gravity. It is a measure of the gravitational force acting on an object, and it varies depending on the object's mass and the strength of the gravitational field it is in.