Physics Chapter 5: Gravity & Momentum
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Questions and Answers

What is the gravitational force between two 60kg masses that are one meter apart?

  • 0.00000048 N
  • 0.000001 N
  • 0.00000012 N
  • 0.00000024 N (correct)

Which of the following statements about momentum is true?

  • Two objects with the same mass moving at the same speed have the same momentum. (correct)
  • Momentum can only exist in objects at rest.
  • All objects in motion have the same momentum regardless of mass.
  • Momentum is independent of an object's mass and velocity.

What reason is given for not observing the gravitational force between ordinary objects?

  • The masses are too small.
  • The forces involved are negligible compared to other forces. (correct)
  • The gravitational constant is too high.
  • The distance between objects is too large.

If a truck and a small car are moving at the same speed, what primarily differentiates their momentum?

<p>Their mass. (B)</p> Signup and view all the answers

Which of the following scenarios demonstrates a change in momentum?

<p>A ball rolling down a hill gaining speed. (A)</p> Signup and view all the answers

What does momentum depend on?

<p>Both mass and velocity (D)</p> Signup and view all the answers

Which unit is correct for measuring momentum?

<p>kg m/s (B)</p> Signup and view all the answers

In an elastic collision, which of the following equations holds true?

<p>m1v1 + m2v2 = m1v1' + m2v2' (C)</p> Signup and view all the answers

What happens to the total momentum when two objects collide?

<p>It stays the same (C)</p> Signup and view all the answers

When calculating the momentum of an object moving with a mass of 1000 kg and a velocity of 16 m/s, what is the momentum value?

<p>16000 kg m/s (C)</p> Signup and view all the answers

Which type of collision is characterized by objects sticking together after the impact?

<p>Inelastic collision (A)</p> Signup and view all the answers

If a car with a mass of 1800 kg travels at 80 m/s, what is its momentum?

<p>1.44 × 10^5 kg m/s (D)</p> Signup and view all the answers

What is the primary reason that objects fall towards the Earth?

<p>There is a force of gravity pulling them downwards. (A)</p> Signup and view all the answers

What does the law of inertia state about an object's motion in the absence of external forces?

<p>It will remain at rest or continue moving at a constant velocity. (C)</p> Signup and view all the answers

Why does the moon not fall straight towards the Earth despite the gravitational pull?

<p>It moves with a sideways speed. (A)</p> Signup and view all the answers

If the gravitational force between the sun and its planets were to disappear, what would happen to the planets?

<p>They would move in straight lines at constant speeds. (B)</p> Signup and view all the answers

What aspect of an object is NOT changed by the gravitational force while it is falling?

<p>The direction of the falling object. (B)</p> Signup and view all the answers

What is the significance of the speed of a falling object in relation to gravitational force?

<p>It determines how quickly the object will hit the ground. (C)</p> Signup and view all the answers

What happens to the force of gravity when an object is released from any altitude?

<p>It remains constant regardless of altitude. (C)</p> Signup and view all the answers

How does the force of gravity influence the motion of an artificial satellite?

<p>It keeps it in orbit while allowing continuous sideways motion. (A)</p> Signup and view all the answers

What is the relationship between the gravitational force and the masses of two objects?

<p>Proportional to the product of the two objects’ masses (B)</p> Signup and view all the answers

Which of the following correctly defines how gravity changes with altitude?

<p>Decreases with increasing distance from the earth's center (B)</p> Signup and view all the answers

What is the acceleration due to gravity at the surface of the earth calculated using the values provided?

<p>9.8 m/s² (C)</p> Signup and view all the answers

Why do a feather and a bowling ball fall at the same rate in a vacuum?

<p>Because the acceleration due to gravity is unaffected by mass (B)</p> Signup and view all the answers

How is weight defined in terms of gravitational force?

<p>The force of gravity that the earth exerts on an object (B)</p> Signup and view all the answers

When calculating weight using the formula $F = \frac{G m M}{r^2}$, what does M represent?

<p>The mass of the earth (D)</p> Signup and view all the answers

If an object weighs 784 N on Earth, what is its mass?

<p>80 kg (A)</p> Signup and view all the answers

What factor is NOT considered when calculating the gravitational force between two objects?

<p>The temperature of the environment (B)</p> Signup and view all the answers

Flashcards

Law of Inertia

An object at rest will stay at rest and an object moving at a constant velocity (constant speed and direction) will continue without change. This applies only in the absence of external influences.

Falling Object & Force

The observation that a falling object's speed increases but its direction stays constant implies that an external force acts on it, pulling it downwards.

Force of Gravity

The force that pulls objects towards the center of the Earth.

Falling vs. Orbiting

Both a falling stone and an orbiting satellite are influenced by the pull of gravity. The difference lies in their initial velocity and the force's effect on their motion.

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Moon's Orbital Motion

The Earth's gravity pulls the moon towards it, but the moon's sideways speed prevents it from falling straight down. This sideways motion causes its orbit.

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Sun's Gravity & Planets

If the force of gravity between the sun and its planets suddenly disappeared, the planets, no longer pulled inward, would continue moving in a straight line at a constant speed.

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Gravity's Influence

The force of gravity between two objects depends on their mass and the distance between them.

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Momentum

Momentum is a measure of an object's motion, taking into account its mass and velocity. It is the product of mass and velocity.

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What is momentum?

Momentum is a measure of an object's motion, taking into account both its mass and velocity. It's essentially how much 'oomph' an object has based on its size and how fast it's moving.

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How do you calculate momentum?

Momentum is calculated by multiplying an object's mass and velocity. The greater the mass or velocity, the greater the momentum.

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Can objects with different masses and velocities have the same momentum?

A large truck moving slowly and a small car moving quickly can have the same momentum if their mass and velocity factors balance out.

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What is the law of conservation of momentum?

Momentum is conserved, meaning the total momentum of a system remains constant in the absence of external forces. In simpler terms, the total amount of 'oomph' in a system stays the same.

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How do you change an object's momentum?

Force is needed to change an object's momentum. The greater the force, the quicker the change in momentum. This is why a strong force is needed to stop a massive truck quickly.

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Newton's Law of Universal Gravity

The attractive force existing between any two objects, directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

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Gravity vs. Altitude

The acceleration due to gravity on Earth decreases as the altitude increases. This is because the force of gravity weakens with distance from Earth's center.

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Acceleration Due to Gravity

The acceleration of a falling object due to Earth's gravity near its surface, calculated using Newton's Law of Universal Gravity.

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Weight

The force exerted by Earth's gravity on an object, calculated using Newton's Law of Universal Gravity and the object's mass.

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Gravity Between People

The force of gravity between two people is extremely small, because their masses are relatively small compared to Earth's mass.

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Gravity & Mass

The acceleration due to gravity does not depend on the mass of the falling object, which means that objects with different masses fall at the same rate in a vacuum.

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Inertia

The ability of an object to resist changes in its motion. This resistance is directly proportional to the object's mass.

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What is an elastic collision?

An elastic collision is a type of collision where the total kinetic energy of the objects involved is conserved. Think of it as a 'no stick' collision.

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What is an inelastic collision?

An inelastic collision is a type of collision where some kinetic energy is lost, typically as heat or sound. Think of a car crash where the cars stick together.

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What is the principle of conservation of momentum in collisions?

In any isolated system, the total momentum before a collision equals the total momentum after the collision. This is another way of stating the law of conservation of momentum.

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Study Notes

Chapter 5: The Law of Gravity & Momentum

  • The Law of Gravity describes the attractive force between any two objects in the universe.
  • This force is proportional to the product of the masses of the two objects.
  • This force is inversely proportional to the square of the distance between the objects.

Why Things Fall: The Idea of Gravity

  • Aristotle believed objects seek the Earth's center.
  • The Law of Inertia states that an object at rest stays at rest and an object in motion at constant velocity stays in motion unless acted upon by an external force.
  • Observation: A falling object's speed keeps changing
  • Consequence: A falling object experiences a constant external force which changes the object's speed.
  • The force that causes objects to fall is called gravity
  • Next, the presentation outlines the nature of gravity.

Falling Versus Orbiting

  • A stone dropped from any height falls to the ground.
  • Artificial satellites move around the Earth due to the pull of Earth's gravity.
  • When a satellite's speed is greater than 7,600 m/s, an object goes into orbit around Earth.
  • When an object’s speed is faster than 11,200 m/s or above, the object leaves the Earth's orbit.
  • Objects slower than 7,600 m/s fall back to Earth.
  • The two types of motion—falling and orbiting—are related.

Orbital Motion of the Moon

  • Earth's gravity pulls the moon towards it.
  • The moon has a sideways speed from its orbit (1.022 km/s).
  • Without the sideways speed, the moon would fall straight down toward Earth.
  • Earth's gravity bends the moon's path as it moves around Earth.

Question: What path do planets take if gravity suddenly disappears?

  • Each planet would move in a straight line, at a constant speed.

Satellite Motion: Balancing Gravity With Speed

  • To put a satellite in orbit, the satellite needs enough sideways speed to counteract the pull of gravity.

The Law of Gravity: Statement

  • Between any two objects, an attractive force exists.
  • The force is proportional to the product of the objects' masses.
  • The force is inversely proportional to the square of the distance between them.
  • The relationship: F = G(m1m2)/r^2.

Earth's Gravity Changes With Altitude

  • Earth's gravitational pull decreases with distance from its center.

Example: Calculating Acceleration Due to Gravity

  • The mass of the Earth (M) is 5.98 × 10^24 kg.
  • The distance between the object and the Earth's center (r) is 6.37 × 10^6 m.
  • The Universal Gravitational Constant (G) is 6.672 × 10^-11 Nm^2/kg^2.
  • Calculating the acceleration due to gravity (a), using the formula a=GM/r^2 -a = 9.8 m/s^2.
    • The acceleration due to gravity near Earth's surface does not depend on the mass of the object. A feather and a bowling ball experience the same acceleration. Removed of air, both items fall at the same rate.

Example Calculation: Weight

  • Assuming a mass of 80kg, weight can be calculated using the formula Weight = (Mass of Earth x Mass of object / Radius squared)x Universal Gravitational Constant
  • Weight is 784 N.

Force of Gravity Between Two People

  • The gravitational force between two people is very small .
  • The formula F = Gm1m2/r2 shows how small the force is between very ordinary objects.

Momentum

  • Momentum is the quantity of motion of an object. it has more momentum when it is bigger and/or it moves faster
  • Momentum of a moving object is directly related to its mass and velocity.
  • Momentum is a vector quantity, the units are kg m/s.

Equivalent Momentum

  • Momentum is the same as the product of mass and velocity
  • Momentum= Mass * Velocity

Conservation of Momentum

  • When objects collide, they exchange momentum, but the total momentum remains constant.

Types of Collisions: Elastic vs. Inelastic

  • Elastic Collision: Objects bounce off each other.
    • Momentum is conserved in an elastic collision.
  • Inelastic Collision: Objects stick together after a collision.
    • Momentum is conserved in an inelastic collision.

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Chapter 5: The Law of Gravity & Momentum PDF

Description

Explore the fundamental concepts of gravity and momentum with this quiz. Learn about the law of gravity, Aristotle's ideas, and the differences between falling and orbiting objects. Test your knowledge on how these forces affect motion and the behavior of different objects in space.

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