Sir Isaac NewtonDiscoveredLaws Of MotionT- 1-855-694-8886Email- info@iTutor.comBy iTutor.com
An object at rest tends to stay at rest and anobject in motion tends to stay in motion unlessacted upon by an unbalanced force. Inertia is the tendency of an object to resistchanges in its velocity: whether in motion ormotionless.
Example- A school bus comes to a sudden stop, and all of the backpacks onthe floor start to slide forward. What force causes them to do that?Answer: No force; the backpacks continue moving untilstopped by friction or collision.
Alternative Statement In the absence of external forces, when viewed from aninertial reference frame, an object at rest remains atrest & an object in motion continues in motion with aconstant velocity Newton’s 1st Law describes what happens in the absence of a netforce.Also tells us that when no force acts on an object, the acceleration ofthe object is zero.
Inertia: The tendency of a body to maintain its state ofrest or motion.Mass: A measure of the inertia of a body,Quantity of matter in a body Quantify mass by having a standardmass = Standard Kilogram (kg) SI Unit of Mass = Kilogram (kg)Weight: The force of gravity on an object
Newton’s second law gives the relationship ofacceleration to force and inertia.Newton’s Second Law: The acceleration of an object is directlyproportional to the net force acting on the object, isin the direction of the net force, and is inverselyproportional to the mass of the object. The acceleration of an object is always in thedirection of the net force.
When objects are changing direction or velocity:If any object is changing direction or velocity (the type of motion), we say the object isaccelerating (the state of motion). This unit will show the concepts behindaccelerations, what causes acceleration (net force),Newtons 2nd Law of Motion.
Experiment : The net force F on a body and the accelerationa of that body are related. Thousands of experiments over hundreds of years find(object of mass m):------- (Proportionality) We choose the units of force so that this is not just aproportionality but an equation:ormfamFamaFF = the net force acting on mass mm = the mass (inertia) of the object.a = acceleration of object.Description effect of F. F is the cause of a.
Example : Force to stop a car.What average net force is required to bring a 1500-kg car torest from a speed of 100 km/h with in a distance of 55 m?In Figure .First, find the acceleration (assumed constant) from the initial and finalspeeds and the stopping distance;a = -7.1 m/s2.Then use Newton’s second law: F = -1.1 x 104 N.
The law of action and reaction. For every action there is an equal and oppositereaction.Whenever one object exerts a force on a secondobject, the second object exerts an equal (inmagnitude) and opposite (in direction) force on thefirst object
Example :Rocket propulsion can also be explained using Newton’sthird law: hot gases from combustion spew out of the tail ofthe rocket at high speeds. The reaction force is what propelsthe rocket.Note that the rocket does not need anythingto “push” against.11In Figure :-The launch of a rocket. The rocket engine pushes thegases downward, and the gases exert an equal andopposite force upward on the rocket, accelerating itupward.(A rocket does not accelerate as a result of itspropelling gases pushing against the ground.)