Gravitational Force

Bozeman Science
19 Jun 201405:00
EducationalLearning
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TLDRIn this AP Physics essentials video, Mr. Andersen explains the concept of gravitational force, the force exerted on objects with mass within a gravitational field, equated to weight on Earth. He clarifies the difference between a balance, which measures mass, and a scale, which measures weight. The gravitational force is calculated by multiplying the mass of an object (in kilograms) by the gravitational field strength (9.8 newtons per kilogram on Earth). The video emphasizes the distinction between objects in free fall and those on Earth's surface, where normal forces come into play.

Takeaways
  • ๐ŸŒ Gravitational force is the force experienced by an object with mass within a gravitational field, which is perceived as weight on Earth.
  • ๐ŸŠ To measure an object's weight (gravitational force), a scale is used, not a balance, which measures mass.
  • ๐Ÿ“ˆ The weight of an object on the Moon would be less due to its weaker gravitational field compared to Earth.
  • ๐Ÿ”„ Gravitational force is a vector that acts in the direction of the gravitational field and can be calculated as the product of mass (m) and the gravitational field strength (g).
  • ๐Ÿ“Š The gravitational field strength on Earth is approximately 9.8 N/kg, which is numerically equal to the acceleration due to gravity (g).
  • ๐Ÿ”ข The force acting on an object due to gravity can be calculated using the formula: F = m * g.
  • ๐Ÿš€ In free fall, an object's acceleration towards Earth is numerically equal to the gravitational field strength.
  • ๐Ÿ›Œ Objects at rest on Earth's surface experience a normal force that balances the gravitational force, which is measured by a scale.
  • ๐Ÿ“ Mass is always measured in kilograms and gravitational field strength in newtons per kilogram.
  • ๐Ÿ‹๏ธโ€โ™‚๏ธ The weight of an object can be found by multiplying its mass in kilograms by the gravitational field strength in newtons per kilogram.
  • ๐Ÿ“ Understanding the concept of gravitational force and its calculation (m * g) is fundamental in physics and helps explain the behavior of objects in gravitational fields.
Q & A

  • What is the difference between gravitational force and weight?

    -Gravitational force is the force experienced by an object with mass when it is in a gravitational field, while weight is the measure of the gravitational force acting on an object on Earth.

  • How can you measure the mass of an object?

    -You can measure the mass of an object using a balance, which measures mass and remains constant regardless of the gravitational field's strength.

  • What device is used to measure weight?

    -A scale is used to measure weight, as it measures the force of gravity acting on an object.

  • What happens to a scale's reading when an object is in free fall?

    -In free fall, a scale would read 0.0 because there is no normal force acting on the object to counteract gravity.

  • How is gravitational force calculated?

    -Gravitational force is calculated by multiplying the mass (m) of an object by the gravitational field strength (g), represented as F = m * g.

  • What is the gravitational field strength on Earth?

    -The gravitational field strength on Earth is 9.8 newtons per kilogram (N/kg).

  • What is the relationship between gravitational field strength and the acceleration due to gravity (g)?

    -On Earth, the gravitational field strength in newtons per kilogram is numerically equal to the acceleration due to gravity (g), but their units are different.

  • How does the gravitational force affect an object in a gravitational field?

    -In a gravitational field, an object will experience a force that causes it to accelerate towards the center of the field (Earth in this case).

  • What is the difference between an object in free fall and one on the planet's surface?

    -An object in free fall is only subject to gravity and will accelerate, while an object on the surface is also subject to the normal force that prevents it from accelerating towards the Earth's center.

  • How would the weight of a 250 kg object be calculated?

    -The weight would be calculated by multiplying the mass (250 kg) by the gravitational field strength (9.8 N/kg), resulting in a force of 2500 newtons.

  • What is the significance of the direction in which gravitational force acts?

    -The direction of the gravitational force is towards the source of the gravitational field (like the center of the Earth), and it is a vector quantity, meaning it has both magnitude and direction.

Outlines
00:00
๐ŸŒ Introduction to Gravitational Force and Weight

This paragraph introduces the concept of gravitational force, which is the force experienced by an object with mass when it is in a gravitational field. On Earth, this force is commonly referred to as weight. The distinction between mass and weight is clarified through the example of measuring an orange's weight with a scale versus its mass with a balance. It explains that while the mass remains constant regardless of location (e.g., Earth or Moon), the weight changes due to the varying strength of the gravitational field. The paragraph emphasizes the importance of measuring gravitational force in newtons and sets the stage for understanding the relationship between mass, gravitational field strength, and the force experienced by an object.

Mindmap
Keywords
๐Ÿ’กgravitational force
Gravitational force is the attractive force that a body with mass experiences when it is in a gravitational field. In the context of the video, this force is what we perceive as weight on Earth. The script explains that gravitational force can be calculated by multiplying the mass of an object (m) by the gravitational field strength (g), and it is measured in newtons.
๐Ÿ’กweight
Weight is the force exerted on an object due to gravity. It is the result of the gravitational force acting on an object's mass. The video clarifies that while mass is a measure of the amount of matter in an object and remains constant, weight can change depending on the gravitational field strength of the environment.
๐Ÿ’กmass
Mass is a measure of the amount of matter in an object, and it is an intrinsic property that does not change regardless of location. In the video, it is emphasized that mass is measured in kilograms and remains constant even when the object is moved to a different gravitational field, such as the Moon.
๐Ÿ’กgravitational field
A gravitational field is the region around a massive object where its gravity affects other objects. The strength of the gravitational field is determined by the mass of the object creating it and is directed towards the center of the massive body. The video explains that on Earth, the gravitational field is uniform enough that we can consider its vectors as parallel.
๐Ÿ’กnewtons
Newtons is the unit of force in the International System of Units (SI), named after Sir Isaac Newton. It is used to quantify the gravitational force acting on an object as well as the weight of an object. The video emphasizes that while mass is measured in kilograms, gravitational force and weight are measured in newtons.
๐Ÿ’กbalance
A balance is a device used to measure the mass of an object by comparing it to known masses. The video clarifies that a balance measures mass, not weight, and thus the mass of an object remains the same whether it is on Earth or the Moon.
๐Ÿ’กscale
A scale measures the weight of an object, which is the force exerted on the object due to gravity. The video explains that a scale measures the weight by measuring the force that the object exerts on the scale's spring, and this measurement can vary depending on the gravitational field strength.
๐Ÿ’กfree fall
Free fall is the motion of an object when it is subject only to gravity, with no other forces acting on it (such as air resistance). In the video, it is mentioned that if an object is in free fall, it experiences an acceleration numerically equal to the gravitational field strength, but it does not accelerate towards the center of the Earth because it is already falling towards it.
๐Ÿ’กacceleration
Acceleration is the rate of change of velocity of an object with respect to time. In the context of the video, it is used to describe the change in velocity of an object falling under the influence of gravity. The gravitational field strength is numerically equal to the acceleration due to gravity (g), which is approximately 9.8 m/s^2 on Earth.
๐Ÿ’กnormal force
The normal force is the force exerted by a surface as it supports the weight of an object resting on it. It acts in the opposite direction to the force of gravity. In the video, it is mentioned that on Earth, the normal force prevents objects from accelerating towards the center of the Earth, balancing out the gravitational force.
๐Ÿ’กvector
A vector is a quantity that has both magnitude and direction. In the context of the video, gravitational force is described as a vector because it has a specific strength (magnitude) and is directed towards the center of the Earth (direction). The gravitational field vectors are considered parallel because of the Earth's large size.
Highlights

Gravitational force is the force experienced by an object with mass when placed in a gravitational field, also known as weight on Earth.

A balance measures mass, not weight, and remains constant even when taken to places with different gravitational fields, such as the moon.

A scale measures weight, which changes with the gravitational field's strength, providing a lower value on the moon due to its weaker gravitational pull.

The weight of an object is calculated by multiplying its mass (in kilograms) by the gravitational field strength (in newtons per kilogram).

On Earth, the gravitational field strength is 9.8 newtons per kilogram, which is numerically equal to the acceleration due to gravity (g).

In free fall, an object's acceleration towards Earth is equal to the gravitational field strength, but on the surface, a normal force counteracts this acceleration.

The force measured by a scale is the normal force exerted by the Earth, which is what we perceive as weight.

Objects in free fall experience weightlessness because the gravitational force is not counteracted by a normal force.

The gravitational force acting on an object can be calculated using the formula: gravitational force = mass (m) times gravitational field strength (g).

Mass is always measured in kilograms and gravitational field strength in newtons per kilogram.

The gravitational field is created by any object with mass, and on Earth, these fields point towards the center of the planet.

For practical purposes, Earth's large size allows us to treat gravitational field vectors as parallel to each other.

The force of gravity on an object can be represented as a vector in the direction of the gravitational field.

An object's weight is the force measured by a scale, which is the result of the gravitational force minus the normal force.

In a physics lab, weight is measured in newtons, reflecting the force exerted on the object by the Earth's gravitational field.

The concept of gravitational force is fundamental to understanding the motion of objects in a gravitational field.

The video provides a clear and straightforward method for calculating gravitational force, emphasizing the simplicity of the m*g formula.

The distinction between mass and weight is crucial for understanding the behavior of objects in different gravitational environments.

Transcripts

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