A system is a collection of objects that are analyzed together.

Define surroundings .

The surroundings are any objects that are not part of the system .

Why can a car be modeled as a single object when applying Newton's second law?

Its internal structure (engine, wheels) is not relevant, so it can be ignored The net force, mass and acceleration can be assumed to act at the car's center of mass

What two conditions decide whether a system is open or closed ?

Whether a net external force acts on the system Whether energy or mass is exchanged between the system and the surroundings

Why is a mass sliding on a rough surface an open system?

Friction acts as an external force , and energy is dissipated to the surroundings as heat, so total mechanical energy and momentum decrease.

A ball falls toward Earth. Why does the ball-Earth system not accelerate?

The gravitational forces between the ball and Earth are internal to the system, so no net external force acts on it.

In an object-Earth system, any force other than the gravitational force is an .......... force.

In an object-Earth system, any force other than the gravitational force is an external force.

True or False? A force between two objects in the same system is an external force.

False. A force between two objects within the system is an internal force. Only forces exerted by objects in the surroundings are external.

Define center of mass .

The center of mass of a system is the point where all of an object's mass can be thought to be concentrated .

How can a system consisting of a single object be modeled?

As a point particle located at the system's center of mass All interactions can be considered to act at the center of mass

Do internal forces change the motion of a system's center of mass ?

No. Interactions between objects within a system do not influence the motion of the system's center of mass.

Where is the center of mass of a symmetrical object located?

On the object's lines of symmetry .

The .......... of a single object acts at its center of mass.

The weight of a single object acts at its center of mass.

True or False? The center of mass of an object always lies inside the object.

False. The center of mass is a hypothetical point , so it can lie outside the body.

AP®PhysicsCollege BoardPhysics 1: Algebra-BasedFlashcardsUnit 2: Force & Translational DynamicsSystems & Center of Mass

Systems & Center of Mass (College Board AP® Physics 1: Algebra-Based): Flashcards

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FrontDescribing Systems
Define system.
FrontDescribing Systems
Why can a car be modeled as a single object when applying Newton's second law?
BackDescribing Systems
Its internal structure (engine, wheels) is not relevant, so it can be ignored
The net force, mass and acceleration can be assumed to act at the car's center of mass

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Cards in this collection (16)

Define system.
A system is a collection of objects that are analyzed together.
Define surroundings.
The surroundings are any objects that are not part of the system.
Why can a car be modeled as a single object when applying Newton's second law?
- Its internal structure (engine, wheels) is not relevant, so it can be ignored
- The net force, mass and acceleration can be assumed to act at the car's center of mass
What two conditions decide whether a system is open or closed?
- Whether a net external force acts on the system
- Whether energy or mass is exchanged between the system and the surroundings
Why is a mass sliding on a rough surface an open system?
Friction acts as an external force, and energy is dissipated to the surroundings as heat, so total mechanical energy and momentum decrease.
A ball falls toward Earth. Why does the ball-Earth system not accelerate?
The gravitational forces between the ball and Earth are internal to the system, so no net external force acts on it.
In an object-Earth system, any force other than the gravitational force is an .......... force.
In an object-Earth system, any force other than the gravitational force is an external force.
True or False?
A force between two objects in the same system is an external force.
False.
A force between two objects within the system is an internal force. Only forces exerted by objects in the surroundings are external.
Define center of mass.
The center of mass of a system is the point where all of an object's mass can be thought to be concentrated.
How can a system consisting of a single object be modeled?
- As a point particle located at the system's center of mass
- All interactions can be considered to act at the center of mass
Do internal forces change the motion of a system's center of mass?
No. Interactions between objects within a system do not influence the motion of the system's center of mass.
Where is the center of mass of a symmetrical object located?
On the object's lines of symmetry.
State the equation for the center of mass along an axis.
${\vec{x}}_{cm} = \frac{\sum_{i} m_{i} {\vec{x}}_{i}}{\sum_{i} m_{i}}$
- ${\vec{x}}_{cm}$ = position of the system's center of mass (m)
- $m_{i}$ = mass of each object (kg)
- ${\vec{x}}_{i}$ = position of each object (m)
How are the magnitude and direction of a 2D center of mass position vector found from its x and y coordinates?
- Magnitude: $r_{cm} = \sqrt{x_{cm}^{2} + y_{cm}^{2}}$
- Direction: $tan θ = \frac{y_{cm}}{x_{cm}}$
The .......... of a single object acts at its center of mass.
The weight of a single object acts at its center of mass.
True or False?
The center of mass of an object always lies inside the object.
False.
The center of mass is a hypothetical point, so it can lie outside the body.

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