Newton's_First_Law_0### and Inertia are foundational concepts in physics. They explain how objects behave when no forces act on them, introducing the idea of inertia as resistance to changes in motion.
These concepts set the stage for understanding motion and forces. They're crucial for grasping more complex ideas in mechanics, like and , which build upon this fundamental principle.
Newton's First Law and Inertia
Newton's first law of motion
States an object at stays at rest and an object in motion stays in motion with constant unless acted upon by an
Implies objects at rest remain at rest unless a net external acts on them (book on a table)
Implies objects in motion continue moving at a constant velocity unless a net external force acts on them (hockey puck sliding on ice)
Describes the relationship between force and motion
Inertia and object mass
Inertia resists any change in an object's motion, including changes to its speed and direction
Greater leads to greater inertia
Higher mass objects require a greater force to change their state of motion (boulder vs. pebble)
Lower mass objects require a smaller force to change their state of motion (feather vs. brick)
Inertia measures an object's tendency to resist changes in its motion
Closely related to an object's
Friction's effect on Newton's law
opposes the motion of an object and can cause it to slow down or stop
With friction, an object in motion will not continue at a constant velocity indefinitely
Friction causes the object to slow down and eventually stop unless a force is continuously applied to counteract it (sliding a box across a rough floor)
With friction, an object at rest will start moving when the applied force overcomes the frictional force (pushing a heavy crate)
Frictional force magnitude depends on the surfaces in contact and the normal force between the objects
Inertial Reference Frames and Equilibrium
Inertial reference frames
A frame of reference where Newton's first law holds true
In inertial frames, an object at rest stays at rest and an object in motion stays in motion with constant velocity unless acted upon by an external force (stationary observer watching a moving car)
Non-inertial reference frames are accelerating frames
Rotating platforms or accelerating elevators
Fictitious forces (centrifugal force) appear to act on objects, causing their motion to deviate from Newton's first law (apparent force pushing you back in an accelerating car)
Reference frame choice is crucial when observing and analyzing motion
Motion can appear different when observed from different reference frames (dropping a ball while on a moving train vs. stationary platform)
Identify whether a reference frame is inertial or non-inertial when applying Newton's laws
Equilibrium conditions in systems
An object is in when the acting on it is zero
For equilibrium, the sum of all forces acting on the object must be zero: ∑F=0
Types of equilibrium:
: An object at rest remains at rest if the net force is zero (a book lying on a table)
: An object in motion continues with constant velocity if the net force is zero (a car moving at a constant speed on a flat road)
To determine equilibrium conditions:
Identify all forces acting on the object
Draw a representing the object and the forces
Set the sum of the forces equal to zero and solve for the unknown quantities
Objects in equilibrium can be balanced or under the action of opposing forces that cancel each other out (a tug-of-war with equal forces on both sides)
Newton's Laws of Motion and Acceleration
Newton's laws of motion
First law: Describes the behavior of objects when no net force acts on them
Second law: Relates force, mass, and acceleration (F = ma)
Third law: States that for every action, there is an equal and opposite reaction
These laws form the foundation for understanding the relationship between forces and motion
Acceleration and force
Acceleration occurs when there is a net force acting on an object
The magnitude of acceleration depends on the net force and the object's mass
Direction of acceleration is the same as the direction of the net force
Key Terms to Review (34)
Acceleration: Acceleration is the rate of change of velocity with respect to time. It represents the change in an object's speed or direction over a given time interval, and is a vector quantity that has both magnitude and direction.
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.
Brownian motion: Brownian motion is the random, erratic movement of particles suspended in a fluid (liquid or gas) resulting from collisions with fast-moving molecules of the fluid. It provides evidence for the kinetic theory of gases and supports the concept of molecular motion.
Dynamic Equilibrium: Dynamic equilibrium is a state of balance in a system where opposing forces or processes are exactly counterbalanced, resulting in no net change over time. This concept is crucial in understanding the behavior of objects under the influence of various forces.
Equilibrium: Equilibrium occurs when all forces acting on an object are balanced, resulting in no net force and no acceleration. In static equilibrium, the object is at rest, and in dynamic equilibrium, it moves with constant velocity.
Equilibrium: Equilibrium is a state of balance or stability, where the forces acting on a system are in balance, and the system is at rest or in a state of constant motion. This concept is fundamental in understanding various physical phenomena, including the behavior of objects, the distribution of forces, and the stability of systems.
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-body diagram: A free-body diagram is a graphical representation used to visualize the forces acting on an object. Each force is represented by an arrow pointing in the direction of the force with its length proportional to the magnitude.
Free-Body Diagram: A free-body diagram is a visual representation of an object or system that shows all the external forces acting on it. It is a fundamental tool used in physics to analyze the forces acting on an object and to solve problems involving Newton's laws of motion.
Friction: Friction is a force that opposes the relative motion between two surfaces in contact. It arises due to the microscopic irregularities on the surfaces, which create resistance to sliding or rolling. Friction is a fundamental concept in physics that plays a crucial role in various topics, including solving problems, understanding forces, and analyzing energy transformations.
Hydrostatic equilibrium: Hydrostatic equilibrium is a state in which the pressure gradient force within a fluid balances the gravitational force acting on that fluid. This balance prevents the fluid from collapsing under its own weight or expanding uncontrollably.
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.
Inertial Reference Frame: An inertial reference frame is a perspective from which the laws of physics hold true, particularly Newton's laws of motion, indicating that an object remains at rest or in uniform motion unless acted upon by an external force. This concept is foundational in understanding motion, as it describes a situation where observers are either at rest or moving at a constant velocity, without experiencing acceleration.
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 inertia: The law of inertia states that an object at rest will remain at rest, and an object in motion will continue in motion with a constant velocity, unless acted upon by a net external force. It is also known as Newton's First Law of Motion.
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.
Momentum: Momentum is a vector quantity that describes the motion of an object. It is defined as the product of an object's mass and its velocity, and it represents the object's quantity of motion. Momentum is a fundamental concept in physics that is closely related to other important topics such as forces, energy, and collisions.
Motion: Motion refers to the change in position of an object over time. It is a fundamental concept in physics that describes the movement of objects in space and the factors that influence their behavior. Motion is a crucial component in understanding various physical phenomena, including the motion of celestial bodies, the motion of everyday objects, and the motion of subatomic particles.
Net force: Net force is the total force acting on an object, taking into account both the magnitude and direction of all individual forces. It determines the object's acceleration according to Newton's second law of motion, which states that an object will accelerate in the direction of the net force. Understanding net force is crucial for analyzing how forces interact and influence motion, as it helps explain concepts like inertia, action-reaction pairs, and equilibrium conditions.
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 first law: Newton's First Law, also known as the law of inertia, states that an object at rest will stay at rest and an object in motion will remain in motion at a constant velocity unless acted upon by a net external force.
Newton's First Law: Newton's First Law, also known as the Law of Inertia, states that an object at rest will remain at rest, and an object in motion will continue moving at a constant velocity, unless acted upon by an unbalanced force. This fundamental principle describes the relationship between an object's state of motion and the forces acting upon it.
Newton's Laws of Motion: Newton's Laws of Motion are a set of three fundamental principles that describe the relationship between an object and the forces acting upon it, governing the motion of objects in the physical world. These laws form the foundation of classical mechanics and are essential in understanding the behavior of objects in various contexts, including the Scope and Scale of Physics, Algebra of Vectors, Free Fall, Newton's First Law, Impulse and Collisions, and Center of Mass.
Non-Inertial Reference Frame: A non-inertial reference frame is a frame of reference that is accelerating or rotating with respect to an inertial frame of reference. In other words, it is a frame that is not in a state of constant velocity or at rest, and thus experiences apparent forces that do not exist in an inertial frame.
Rest: Rest refers to the state of being motionless or inactive, where an object or system is not undergoing any change or movement. In the context of physics, rest is a fundamental concept that underpins Newton's First Law, which describes the behavior of objects in the absence of external forces.
Static Equilibrium: Static equilibrium is a state in which the net force and net torque acting on an object are both zero, resulting in the object remaining at rest or in a constant position. This concept is crucial in understanding the behavior of objects under various physical conditions.
Unbalanced Force: An unbalanced force is a net force acting on an object that causes the object to accelerate or change its motion. It is the difference between the sum of all the forces acting on an object and zero, resulting in a non-zero net force that leads to a change in the object's state of motion.
Uniform Motion: Uniform motion is a type of motion where an object travels at a constant speed, maintaining the same velocity throughout its journey. This means the object covers equal distances in equal intervals of time, with no acceleration or deceleration involved.
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.
Velocity: Velocity is a vector quantity that describes the rate of change of an object's position with respect to time. It includes both the speed and the direction of an object's motion, making it a more complete description of an object's movement compared to just speed alone.