Forces shape our physical world, from the keeping us on the ground to tension in ropes and cables. Understanding these common forces helps us analyze everyday situations and complex systems, connecting the abstract concepts to tangible experiences.
Newton's_Laws_0### provide a framework for understanding motion and interactions between objects. By applying these laws to real-world scenarios, we can predict and explain the behavior of objects under various forces, bridging the gap between theory and practical applications.
Common Forces
Normal and tension forces
acts perpendicular to surface of contact prevents object from sinking into surface (book on table, person standing on ground)
Magnitude of normal depends on weight of object and surface properties (hardness, elasticity)
exerted by rope, string, cable when pulled taut always along length of object (person hanging from rope, clothesline with clothes)
Magnitude of tension force equal at both ends of object determined by weight of suspended object and angle of rope
Real vs fictitious forces
Real forces exist in nature caused by interaction between objects (gravitational, electromagnetic, strong and weak nuclear)
apparent due to of reference frame do not exist in inertial reference frame
appears to push objects away from center of rotation (person in rotating car pushed against door)
deflects moving objects in rotating reference frame (wind patterns on Earth affected by rotation)
useful for analyzing motion in non-inertial reference frames (rotating platforms, accelerating vehicles)
Newton's laws in complex systems
(): object maintains state of rest or constant velocity unless acted upon by net external force ()
: Fnet=ma, acceleration directly proportional to net force inversely proportional to
: action-reaction force pairs equal in magnitude opposite in direction act on different objects
Solving problems with multiple forces:
Identify all forces acting on object
Draw representing object and forces (force)
Choose coordinate system (x and y axes)
Resolve forces into components along chosen axes
Apply Newton's 2nd law to each axis separately (∑Fx=max, ∑Fy=may)
Solve resulting equations for desired quantities (acceleration, tension, normal force)
Examples:
Block on inclined plane with friction (normal force, , )
Atwood machine with unequal masses (tension forces, gravitational forces)
Friction and Work-Energy
Friction is a force that opposes motion between surfaces in contact
prevents objects from starting to move (static friction)
acts on objects already in motion (kinetic friction)
is done when a force moves an object over a distance (work)
is the capacity to do work and comes in various forms (energy)
Key Terms to Review (37)
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.
Centrifugal force: Centrifugal force is a fictitious force perceived in a rotating reference frame, directed outward from the axis of rotation. It arises due to the inertia of an object moving in a curved path.
Centrifugal Force: Centrifugal force is an apparent force that acts on an object moving in a circular path, directing the object away from the center of the circle. It is a result of the object's inertia, which causes it to resist changes in its direction of motion.
Coefficient of kinetic friction: The coefficient of kinetic friction is a dimensionless constant that represents the ratio of the force of kinetic friction between two bodies in relative motion to the normal force pressing them together. It is denoted by $\mu_k$.
Coriolis Force: The Coriolis force is an apparent force that acts on objects in motion relative to a rotating reference frame, such as the Earth. It is responsible for the deflection of moving objects, including air masses and ocean currents, in the Northern and Southern Hemispheres.
Electromagnetic Force: The electromagnetic force is one of the four fundamental forces in nature, along with the strong nuclear force, the weak nuclear force, and gravity. It is the force that governs the interactions between electrically charged particles, manifesting as both electric and magnetic fields.
Energy: Energy is the fundamental quantity that describes the ability to do work or cause change. It is the driving force behind all physical and chemical processes in the universe, from the smallest subatomic interactions to the largest-scale cosmic events. Energy can take many forms, such as kinetic, potential, thermal, electrical, and more, and it is conserved in the sense that it cannot be created or destroyed, only transformed from one type to another.
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.
Fictitious forces: Fictitious forces, also known as pseudo-forces, arise when observing motion from a non-inertial reference frame. They do not result from any physical interaction but are perceived due to the acceleration of the reference frame itself.
Fictitious Forces: Fictitious forces, also known as pseudo-forces, are apparent forces that arise in a non-inertial reference frame, such as a rotating or accelerating frame of reference. These forces are not real physical forces, but rather mathematical constructs that are introduced to simplify the analysis of motion in non-inertial frames.
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 Force: Friction force is the force that opposes the relative motion between two surfaces in contact. It arises due to the microscopic irregularities and interactions between the surfaces, causing resistance to their sliding or rolling motion.
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.
Kinetic Friction: Kinetic friction is the force that opposes the relative motion between two surfaces in contact. It acts in the direction opposite to the direction of motion, and its magnitude is independent of the area of contact between the surfaces.
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.
Net work: Net work is the total work done on an object, accounting for all forces acting on it. It determines the change in the object's kinetic energy.
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 1st 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 to move at a constant velocity, unless acted upon by an unbalanced force.
Newton's 2nd Law: Newton's second law of motion states that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass. It describes the relationship between an object's motion and the forces acting upon it.
Newton's 3rd Law: Newton's 3rd law, also known as the law of action and reaction, states that 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 and opposite force on the first object.
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: The normal force is the perpendicular contact force exerted by a surface on an object in contact with it. It acts perpendicular to the surface and counteracts the component of other forces acting in that direction.
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.
Static Friction: Static friction is the force that acts between two surfaces in contact with each other, preventing them from sliding relative to one another. It arises from the microscopic irregularities on the surfaces and the adhesive forces between them, and it opposes the tendency of the surfaces to slide.
Strong Nuclear Force: The strong nuclear force is one of the four fundamental forces in nature, along with gravity, electromagnetism, and the weak nuclear force. It is the force that binds protons and neutrons together within the nucleus of an atom, holding the nucleus together despite the repulsive force between the positively charged protons.
Tension Force: Tension force is a type of contact force that acts between two objects that are connected by a string, rope, cable, or some other medium. It is the force that pulls on an object, keeping it from moving away from the point of attachment.
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.
Weak Nuclear Force: The weak nuclear force is one of the four fundamental forces in nature, responsible for certain types of radioactive decay. It is much weaker than the strong nuclear force and acts over an extremely short range, governing the interactions between subatomic particles such as quarks and leptons.
Work: Work is a physical quantity that describes the energy transferred by a force acting on an object as the object is displaced. It is the product of the force applied and the displacement of the object in the direction of the force.