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2.4 Newton's First Law

#inertialmass

#gravitationalmass

#equilibrium

#frameofreference

โฑ๏ธย ย 3 min read

written by

Peter Apps

peter apps

June 8, 2020


Essential Knowledge 1.C.1 ๐Ÿ˜

Inertial mass is the property of an object or system that determines how its motion changes when it interacts with other objects or systems.

Newtonโ€™s First Law states, โ€œevery object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.โ€ Another term for this law is the Law of Inertia because it explains the concept that objects have the tendency to resist a change in motion. It is also commonly referred to as just a special case of Newtonโ€™s Second Law when the net external force is zero.

Key Concept: Frame of Reference: A coordinate system in relation to which judgments can be made, usually from an observerโ€™s point of view, is known as a frame of reference. A frame of reference moving with constant velocity is known as an inertial frame of reference. ๐Ÿ™‹โ€โ™€๏ธ๐Ÿ™‹โ€โ™‚๏ธ

Key Concept: Inertial Mass - the ability of an object to resist a change in its state of motion. The inertia of an object is measured based on its mass.ย 

  • An object with a small mass will exhibit less inertia and be more affected by other objects, and an object with a large mass will exhibit greater inertia and be less affected by other objects.

Thatโ€™s why it would be a lot harder to move an elephant from rest than an ant! Simply put, inertial mass is a measure of how difficult it is to change the uniform motion of an object by an external force. (๐Ÿœ < ๐Ÿ˜)

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Image courtesy of WikiHow.

As shown in the image above, the force of the person, given by mass x acceleration, is equal to Fnet because it is the only unbalanced force. However, if the sum of the forces acting on the object is zero then the system would be in equilibrium.ย  Key Concept: Equilibrium - when the vector sum of the forces acting on an object is equal to zero

Essential Knowledge 1.C.3 ๐Ÿ

Objects and systems have properties of inertial mass and gravitational mass that are experimentally verified to be the same and that satisfy conservation principles.

Key Concept: Gravitational Mass - determined by the strength of the gravitational force experienced by the body when in the gravitational field g.

Equation:

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Gravitational Mass vs. Inertial Mass

  • Gravitational mass is measured by comparing the force of gravity of an unknown mass to the force of gravity of a known mass.

  • Inertial mass is found by applying a known force to an unknown mass, measuring the acceleration, and applying Newton's Second Law, a = F/m.

Equation:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-08%20at%201.30.19%20PM.png?alt=media&token=82e2ef3d-f22a-448e-adcf-ba87976be3b6

While these masses are measured in varying applications, they have been experimentally proven to equal the same value; therefore Inertial = Gravitationalย 

๐ŸŽฅWatch: AP Physics 1 - Unit 2 Streams

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