Newton's Laws of Motion

Newton's Laws

• Newton's laws are explained

Law of Inertia (Newton's First Law)

• A body maintains a state of rest or constant velocity unless acted upon by an external force.
• A motionless object remains motionless without a net force acting on it.
• A body traveling at a constant speed in a straight path continues its motion unless acted on by a net force that alters speed or direction.
• Inertia gives a skater a tendency to continue gliding with constant speed and direction.

Law of Acceleration (Newton's Second Law)

• Force applied to a body causes acceleration proportional to the force magnitude, in the force direction, and inversely proportional to the body's mass.
• The formula for the law of acceleration is F = ma, where F is Force, m is mass, and a is acceleration.
• A 1-kg ball struck with a 10 N force accelerates at 10 m/s².
• A 2-kg ball struck with a 10 N force accelerates at 5 m/s².

Momentum

• Momentum is a mechanical quantity important in interactions between bodies, especially in collisions.
• Momentum is generally the quantity of motion an object possesses.
• Linear momentum is the product of an object's mass and velocity, expressed as M(P) = mv.

Impulse

• External forces change momentum in a system predictably.
• Changes in momentum depend on the magnitude of external forces and the time over which they act.
• Impulse is the product of force and time, expressed as impulse = Ft.

Linear Impulse-Momentum Relationship

• Linear momentum of an object, like a moving car, changes by applying force over time.
• A quick change in momentum, such as during an emergency stop, requires a large brake force applied for a short time.
• Less brake force for the same time, or the same brake force for even less time, results in a smaller change in momentum.
• Impulse and momentum are vector quantities.
• Impulse acting on a system results in a change in the system's total momentum.
• The relationship between impulse and momentum is derived from Newton's second law.
• F = ma, F = m(v2 – v1)/t, Ft = (mv)2 – (mv)1, Ft= △ M

Law of Reaction (Newton's Third Law)

• For every action, there is an equal and opposite reaction.
• When one body exerts a force on a second, the second body exerts a reaction force equal in magnitude and opposite in direction to the first body.
• If a 90-kg ice hockey player collides head-on with an 80-kg player, and the first player exerts a force of 450 N on the second player, the force exerted by the second player on the first is 450 N in the opposite direction.

Angular Momentum

• At rest, momentum is zero.
• During motion, momentum = mxv.
• L= Ιxω
• I= mxr(k)2 kg.m2
• For the equation Τ=Ιxα, I is the moment of inertia, and α is angular acceleration.
• For a given torque, an object with a larger moment of inertia has a smaller angular acceleration, and vice versa.

Friction

• Friction is defined as F = μR, where μ is the coefficient of friction and R is the normal (perpendicular) reaction force.
• The coefficient of friction is a number serving as an index of interaction between two surfaces in contact
• Normal reaction force acts perpendicular to two surfaces in contact.
• Maximum static friction is the greatest amount of friction generated between two static surfaces.
• Kinetic friction is friction with a constant magnitude, generated between two surfaces in contact during motion.
• A greater contact surface area does not necessarily generate more friction.

Work

• No movement, no work.
• Work is defined as force applied against a resistance, multiplied by its displacement in the direction of the force.
• W = Fd (joule (J))
• A body moved a given distance by an applied external force has work performed on it.
• The work is equal to the product of the applied force's magnitude and the distance through which the body moved.
• Concentric contraction means work is positive.
• Eccentric contraction means work is negative.
• Isometric contraction means the work is zero.
• Performing positive mechanical work typically requires greater caloric expenditure than negative mechanical work.

Power

• Power refers to the amount of mechanical work performed in a given time
• power = work/ change in time
• P = W/Δt and P = FV
• Units of power are units of work divided by units of time.
• Joules divided by seconds are termed watts (W); 1 W = 1 J/s.
• Athletes exerting mechanical power and combining force and velocity is critical to successful performance.
• Peak power is strongly associated with maximum isometric strength.

Mechanical Energy

• Energy is defined as the capacity to do work.
• Mechanical energy is the capacity to do mechanical work
• Units of mechanical energy are the same as units of mechanical work (joules).
• Two forms of mechanical energy: kinetic and potential.

Kinetic Energy

• Kinetic energy (KE) is the energy of motion.
• A body possesses kinetic energy only when in motion.
• Kinetic energy of linear motion is one-half of a body's mass multiplied by the square of its velocity: KE = 1/2 mv2.
• A motionless body (v = 0) has zero kinetic energy.
• Increases in a body's velocity create large increases in kinetic energy.

Potential Energy

• Potential energy (PE) is the energy of position (stored energy).
• Potential energy is a body's weight multiplied by its height above a reference surface: PE = (m.g.h) wt * h.

Work-Energy Relationship

• An object's kinetic energy is changed by a force applied over a displacement.
• A quick change in kinetic energy requires a large brake force over a short displacement.
• Less brake force for the same displacement results in a smaller change in kinetic energy.
• The change in kinetic energy is caused by a force applied over a given displacement.
• The work of a force is equal to the change in energy that it produces in the object acted on.