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Questions and Answers
An object is at rest on a surface. A force is applied, but the object remains stationary. Which statement best describes the friction acting on the object?
An object is at rest on a surface. A force is applied, but the object remains stationary. Which statement best describes the friction acting on the object?
- The friction force is greater than the applied force.
- The friction force is equal to the applied force. (correct)
- The friction force is equal to the maximum possible friction force.
- The friction force is zero.
A car is driving at a constant velocity on a flat, straight road. What can be said about the forces acting on the car?
A car is driving at a constant velocity on a flat, straight road. What can be said about the forces acting on the car?
- The driving force is less than the opposing forces (air resistance and friction).
- There are no forces acting on the car.
- The driving force is greater than the opposing forces (air resistance and friction).
- The driving force is equal to the opposing forces (air resistance and friction). (correct)
A box is sliding down a ramp at a constant speed. What can be concluded about the forces acting on the box?
A box is sliding down a ramp at a constant speed. What can be concluded about the forces acting on the box?
- There is no net force acting on the box.
- The normal force is equal to the weight of the box.
- The component of gravity acting down the ramp is greater than the kinetic friction force.
- The component of gravity acting down the ramp is equal to the kinetic friction force. (correct)
A person lifts a box. Considering the concepts of 'center of mass' and 'center of gravity', which of the following is the most accurate description?
A person lifts a box. Considering the concepts of 'center of mass' and 'center of gravity', which of the following is the most accurate description?
A seesaw is perfectly balanced with two people of different weights sitting on it. Which statement must be true?
A seesaw is perfectly balanced with two people of different weights sitting on it. Which statement must be true?
A door is easier to open when you push on it further from the hinges rather than closer to the hinges. Why?
A door is easier to open when you push on it further from the hinges rather than closer to the hinges. Why?
A crane is lifting a heavy load. If the crane's cable is a lever, what class of lever would it be considered, and why?
A crane is lifting a heavy load. If the crane's cable is a lever, what class of lever would it be considered, and why?
An object is dropped from a height. Which of the following statements accurately describes the object's acceleration as it falls, considering air resistance?
An object is dropped from a height. Which of the following statements accurately describes the object's acceleration as it falls, considering air resistance?
Two objects with masses $m_1$ and $m_2$ are separated by a distance $R$. According to Newton's Law of Universal Gravitation, what happens to the gravitational force between them if the distance $R$ is doubled?
Two objects with masses $m_1$ and $m_2$ are separated by a distance $R$. According to Newton's Law of Universal Gravitation, what happens to the gravitational force between them if the distance $R$ is doubled?
An astronaut is on a planet with twice the mass of Earth and the same radius as Earth. How does the gravitational acceleration on this planet ($g_p$) compare to the gravitational acceleration on Earth ($g_E$)?
An astronaut is on a planet with twice the mass of Earth and the same radius as Earth. How does the gravitational acceleration on this planet ($g_p$) compare to the gravitational acceleration on Earth ($g_E$)?
Flashcards
Centre of Gravity/Mass
Centre of Gravity/Mass
The point through which the entire weight of an object appears to act.
Friction
Friction
Force resisting motion between surfaces.
Friction direction
Friction direction
Friction is the force between two surfaces, parallel to the surfaces.
Maximum Static Friction
Maximum Static Friction
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Air Resistance
Air Resistance
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Terminal Velocity
Terminal Velocity
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Lever
Lever
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Law of the Lever
Law of the Lever
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Principle of Moments
Principle of Moments
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Gravitational Force
Gravitational Force
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Study Notes
- Lecture focuses on types of force: centre of mass, friction, air resistance, levers (classes 1, 2, and 3), fundamental forces, and gravity.
Centre of Gravity or Centre of Mass
- Every object has a point through which its entire weight (mg) appears to act.
- A large object comprises many parts, each with its own gravitational force acting downwards.
- Instead of treating each part separately, the entire weight can be considered acting through a single point.
- The demonstrations of finding centre of gravity involves suspending (hanging) an object freely and using a plumb bob to find the vertical line.
- The intersection of these lines determines the centre of gravity.
Friction
- Friction resists motion between two surfaces and operates parallel to the surfaces.
- Friction opposes relative motion.
- At rest or constant velocity, the friction force (f) equals the pulling force (Fpull).
- The maximum static friction force fmax between two surfaces is proportional to the normal reaction force (N) and the co-efficient of friction (μ): fmax = μN.
- The normal reaction is often equal to the objects weight N = mg, but not always.
- The coefficient of friction denoted by the symbol μ, normally has a value of less than 1 (μ < 1).
- In animal joints, the value of μ is much less then 1, μ <<1.
- Friction is independent of the area of contact.
- Friction depends only on the magnitude of the normal force (N) and the nature of the surfaces in contact.
Atmospheric Friction ('Air Resistance')
- Objects moving rapidly through the air experience a drag force.
- Drag force occurs because the air is pushed away.
- When an object is dropped, acceleration is g = 9.8 m s-2
- Atmospheric friction increases as velocity increases.
- When atmospheric friction equals the weight (mg), the net force becomes zero, and the object stops accelerating.
- The object reaches terminal velocity (VT).
Law of the Lever (Principle of Moments)
- At balance, in equilibrium, the effort multiplied by the effort arm equals the load multiplied by the load arm: F1d1 = F2d2
- The moment of force or torque is Fd, and is a measure of the twisting/turning effect.
- At equilibrium, the sum of clockwise moments equals the sum of anti-clockwise moments.
Classes of Lever
- Levers are divided into 3 classes based on fulcrum position.
- Class 1: fulcrum is between the load and effort.
- Class 2: effort - load - fulcrum (e.g., ankle).
- Class 3: load - effort - fulcrum (e.g., elbow).
Fundamental Forces
- Forces in everyday life are composite, a superposition of fundamental forces which include:
- Electromagnetic Force
- Gravitational Force
- Strong Nuclear Force
- Weak Nuclear Force
Gravitation
- Newton discovered that any mass (m1) attracts any other mass (m2) with a gravitational force (F).
- F=G(m1m2)/R^2
- Where R is the distance between the centres of the masses.
- Where G= 6.67 x 10-11 N m² kg-2
Acceleration Due to Gravity
- A mass (m) is attracted by Earth's mass (ME).
- The mass of Earth is ME = 5.98 x 1024 kg, radius is RE = 6380 km
- g = (GME)/R^2 = 9.80 m s-2
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