Understanding Forces and Motion
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Questions and Answers

Which of the following is NOT an effect of force on an object?

  • Changing the direction of a moving object
  • Increasing the object's mass (correct)
  • Making a moving object stop
  • Making a stationary object move

Field forces require physical contact between two objects.

False (B)

What is the SI unit of force, and what is its formula based on mass and acceleration?

newton, F = ma

An object's tendency to resist changes in its state of motion is called ______.

<p>inertia</p> Signup and view all the answers

Match the following concepts with their descriptions:

<p>Contact Force = Force resulting from physical contact between objects. Field Force = Force that acts at a distance without physical contact. Newton's First Law = An object's motion remains constant unless acted upon by a net external force. Force Diagram = Visual representation of forces acting on an object.</p> Signup and view all the answers

Which of the following best describes the normal force?

<p>The force exerted by a surface on an object, perpendicular to the surface. (B)</p> Signup and view all the answers

According to Newton's first law, what happens to an object in motion if no net external force acts on it?

<p>It continues in motion with constant velocity. (D)</p> Signup and view all the answers

Why is force considered a vector quantity?

<p>Because it has both magnitude and direction. (A)</p> Signup and view all the answers

Kinetic friction is typically greater than static friction.

<p>False (B)</p> Signup and view all the answers

What is the purpose of drawing a free-body diagram when analyzing forces acting on an object?

<p>analyze a situation or problem</p> Signup and view all the answers

What Greek letter is used to represent the coefficient of friction?

<p>mu</p> Signup and view all the answers

The frictional force is the product of the coefficient of friction and the _______ force.

<p>normal</p> Signup and view all the answers

Which of the following statements best describes inertia?

<p>An object's tendency to resist changes in its state of motion. (D)</p> Signup and view all the answers

A crash-test dummy is thrown forward with a force of 200.0 N and hit from behind with a force of 4000.0 N. What net force does the sensor report?

<p>3800.0 N (B)</p> Signup and view all the answers

An object in motion will eventually slow down and come to a stop on its own due to inertia.

<p>False (B)</p> Signup and view all the answers

A box is pushed with a force of 20N to the right and a frictional force of 5N opposes the motion. What is the net force acting on the box?

<p>15N to the right</p> Signup and view all the answers

A book is placed on an inclined drafting table. If the force of the table on the book is 20 N and the force of gravity on the book is 25 N, which of the following statements must be true?

<p>The net force on the book is zero if it remains stationary. (A)</p> Signup and view all the answers

An apple falls from a tree with a gravitational force of 3.0 N downward, and the wind exerts a force of 1.5 N to the right on the apple. Determine magnitude of the net force of this system.

<p>3.35 N</p> Signup and view all the answers

Weight is a force exerted on a body by ______.

<p>gravity</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>Inertia = Resistance to change in motion Net Force = Vector sum of all forces acting on an object Weight = Force exerted on a body by gravity Normal Force = Force perpendicular to a contact surface</p> Signup and view all the answers

Newton's Second Law states that the acceleration of an object is ___________ proportional to the net force acting on the object and inversely proportional to the object's mass.

<p>directly</p> Signup and view all the answers

A 10 kg object experiences a net force of 20 N. What is the object's acceleration?

<p>2 m/s² (B)</p> Signup and view all the answers

Which of the following is true regarding the normal force?

<p>It is always perpendicular to the surface of contact. (B)</p> Signup and view all the answers

Weight is a scalar quantity that depends only on mass.

<p>False (B)</p> Signup and view all the answers

A car of mass $m$ is acted upon by a force $F$ resulting in an acceleration $a$. If the mass of the car is doubled and the force is halved, what is the new acceleration?

<p>$a/4$ (A)</p> Signup and view all the answers

According to Newton's Third Law, if a person pushes against a wall, the wall will not exert a force back on the person because the wall is stationary.

<p>False (B)</p> Signup and view all the answers

A box is at rest on a horizontal surface. Define the 'normal force' acting on this box and describe its direction.

<p>The normal force is the force exerted by the surface supporting the box. It acts perpendicular to the surface, pointing upwards, opposing the force of gravity.</p> Signup and view all the answers

The force of __________ opposes the motion or attempted motion of an object.

<p>friction</p> Signup and view all the answers

Match the type of friction with its description:

<p>Static friction = The force that resists the initiation of movement between two surfaces in contact. Kinetic friction = The force that opposes the movement of two surfaces already in motion.</p> Signup and view all the answers

A 10 kg box is being pushed across a horizontal floor with a constant velocity. The coefficient of kinetic friction between the box and the floor is 0.25. What is the magnitude of the applied force needed to maintain this constant velocity?

<p>24.5 N (B)</p> Signup and view all the answers

A 5 kg block is sitting at rest on a table. The coefficient of static friction between the block and the table is 0.5. You exert a horizontal force on the block. What is the maximum force can you apply before the block starts to move?

<p>24.5 N (B)</p> Signup and view all the answers

A person is trying to move a heavy crate across a floor. They apply a force but the crate doesn't move. Explain why, in terms of forces acting on the crate.

<p>The crate doesn't move because the applied force is equal to or less than the force of static friction. Static friction opposes the applied force, preventing the crate from moving until the applied force exceeds the maximum static friction force.</p> Signup and view all the answers

A box slides down a ramp at a constant acceleration. What forces primarily influence the box's motion?

<p>Gravity, normal force, and kinetic friction (A)</p> Signup and view all the answers

The coefficient of static friction is always less than the coefficient of kinetic friction for the same two surfaces.

<p>False (B)</p> Signup and view all the answers

Explain how increasing the angle of an inclined plane affects the normal force acting on an object resting on the plane.

<p>As the angle increases, the normal force decreases.</p> Signup and view all the answers

When an object is in equilibrium on an inclined plane, the component of gravitational force acting down the plane is equal to the force of ______.

<p>static friction</p> Signup and view all the answers

Match the following scenarios with the type of friction primarily involved:

<p>A box starts to slide down a ramp = Static Friction A box is already sliding down a ramp = Kinetic Friction A car’s tires locked as it skids to a halt = Kinetic Friction</p> Signup and view all the answers

A 30kg box is pulled to the right with a rope that forms a 30 degrees angle with the surface. The force applied is 150N and the coefficient of kinetic friction is 0.25. What is the magnitude of the normal force?

<p>$30 \text{ kg} \cdot 9.8 \text{ m/s}^2 - 150 \text{ N} \cdot \sin(30)$ (A)</p> Signup and view all the answers

A student performs an experiment to measure the coefficient of static friction between a wooden block and an inclined plane. Which of the following actions would improve the accuracy of the experiment?

<p>Measuring the angle at which the block begins to slide multiple times and calculating the average (D)</p> Signup and view all the answers

During the friction lab, a student measures the angle at which a cube begins to slide on an inclined plane. Describe the steps to calculate the coefficient of static friction ($\mu_s$) from this angle ($\theta$).

<p>$\mu_s = \tan(\theta)$</p> Signup and view all the answers

Flashcards

What are Forces?

Interactions between an object and its environment.

How Forces Change Motion?

  1. Start motion, 2. Stop motion, 3. Change direction.

What is a Newton?

The SI unit of force.

What are Contact Forces?

Forces that occur when objects are physically touching.

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What are Field Forces?

Forces that act without physical contact between objects.

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What is a Force Diagram?

A representation showing forces acting on an object with arrows.

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What is a Free-Body Diagram?

A diagram that isolates an object and shows all forces acting on it.

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What is Newton's First Law?

An object maintains its state of motion unless acted upon by a net force.

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Inertia

The tendency of objects to resist changes in their state of motion.

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Newton's First Law (Law of Inertia)

An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

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Net Force

The vector sum of all forces acting on an object.

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External Force

A single force exerted on an object due to interaction with its environment.

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Describing Force

Force is described by its strength and direction.

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Net Force (Effect on Motion)

The combination of all forces acting on an object. Determines if and how an object will accelerate.

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Weight

The force exerted on a body by gravity.

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Normal Force (N)

Force that is always perpendicular to the contact surface.

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Normal Force

The force exerted by a surface on an object, opposing its movement across or effort to move across it.

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Force of Friction

A force that opposes the motion of an object.

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Static Friction (Fs)

Friction when an object is not moving.

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Kinetic Friction (Fk)

Friction when an object is moving.

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Coefficient of Friction (μ)

A value showing how much friction depends on the surfaces in contact.

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Newton's Second Law

The net force is equal to the mass of the object times its acceleration.

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Fnet = ma

The net force on an object is the product of its mass and acceleration.

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Newton's Third Law

Newton's Third Law states that when two objects interact, the force exerted on object 1 by object 2 is equal in magnitude and opposite in direction to the force exerted on object 2 by object 1.

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Weight Calculation

Weight is the force on an object due to gravity and can be calculated using: weight = mass × gravitational acceleration (w = mg).

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Coefficient of Friction

The coefficient of friction (μ) is the ratio of the frictional force to the normal force. It is determined experimentally. Equation: μ = frictional force / normal force

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Static Friction

Static friction is the force that prevents an object from starting to move. It is typically greater than kinetic friction.

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Kinetic Friction

Kinetic friction is the force that opposes the motion of a moving object.

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Static vs. Kinetic Friction

The coefficient of static friction (μs) is the ratio of the maximum static frictional force to the normal force. It is always greater than the coefficient of kenetic friction.

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Free Body Diagram (FBD)

A diagram showing all forces acting on an object.

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Friction Force

The force that opposes motion (or attempted motion) between surfaces.

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Angle of Repose

The angle at which an object starts to slide down an inclined plane. Used to determine the coefficient of static friction.

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Gravity Component (Parallel)

The component of gravity acting parallel to the inclined plane; causes the object to slide down.

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Study Notes

  • Understanding the effect of force on an object's motion is key to understanding physics

Force Defined

  • Forces characterize the interactions between an object and its environment

Force and Motion

  • Forces can change motion in three ways:
  • Setting a stationary object in motion
  • Bringing a moving object to a halt
  • Modifying the direction of a moving object

SI Unit of Force

  • The newton is the SI unit of force.
  • 1 N is equivalent to 1 kg*m/s².
  • The formula F=ma relates force, mass, and acceleration
  • One newton (N) is the force required to accelerate a 1 kg mass at 1 m/s².

Types of Forces

  • Forces can act through physical contact or at a distance
  • Contact forces arise from physical interactions, an example is a stretched spring
  • Field forces do not involve physical contact between two objects.
  • Earth’s gravity accelerates objects downwards
  • Attraction and repulsion interactions occur between electric charges.
  • Electromagnetic fields can also exert force at a distance

Field Forces

  • Field forces, also known as non-contact or action-at-a-distance forces, are exerted without direct contact.

Force Diagrams

  • A force's impact is determined by the magnitude and direction.
  • Force is a vector quantity
  • In force diagrams the object is centered, and all forces acting on the object are shown with arrows.
  • Free-body diagrams help analyze a situation or problem

Quick Lab Example

  • Modeling a car colliding with a brick wall can be done using different balls and a book.
  • Changes in motion can be due to speed and direction
  • Identifying the forces involved allows for the creation of a force diagram

Isaac Newton

  • Isaac Newton (1642–1726) is widely recognized as one of history's most influential scientists.
  • His book is titled: Philosophiae Naturalis Principia Mathematica, published in 1687.
  • Newton formulated laws of motion and universal gravitation.
  • He was born in the same year that Galileo died

Newton's First Law (Law of Inertia)

  • An object maintains its state of rest or constant velocity unless acted upon by a net external force.
  • Inertia is the tendency to maintain the current state of motion or rest of matter

Net Force

  • The vector sum of all forces acting on an object dictates the net force.
  • An external force is a single force that affects an object as a result of interaction with its environment

Nature of Force

  • A misconception is that any object set in motion will slow down on its own
  • The fact however, is that a force is needed to change an object's state of motion

Describing Forces

  • A force is described by its strength and direction
  • Arrows represent the direction and strength of a force
  • The SI unit for Force is the Newton (N)

Forces Impacting Motion

  • The combination of forces on objects at the same time is called "net force."
  • Net force determines if and how an object accelerates
  • A non zero net force means an object's motion will change

Everyday Forces

  • Weight is a scalar quantity
  • Weight is the measurement of the force exerted on an object by gravity
  • Weight is calculated using the formula w=mg
  • Weight is dependent on location
  • Normal force (N) is always perpendicular to the contact surface
  • The force exerted by a surface as an object moves or attempts to move across it is friction
  • Friction opposes the motion of an object.
  • Two types of friction exist:
  • Static friction, Fₛ
  • Kinetic friction, Fₖ

Static and Kinetic Friction

  • Static friction is opposite the push to prevent motion
  • Kinetic friction is opposite the motion

Coefficient of Friction

  • It expresses the dependence of frictional forces on surfaces in contact
  • Greek letter mu (μ) represents mu
  • Ff = µFn , Fn = Normal force
  • μₛ = Fₛ,max / Fn (Static Friction)
  • μₖ = Fk / Fn (Kinetic Friction)

Example Quick Lab

A small ball on a skateboard is influenced by friction, observe what happens, explain with inertia concept

Net Force

  • A crash-test dummy's torso sensor records the net force's magnitude and direction.

Determining Net Force at an Angle

  • The book lies on the table inclined, diagram needed of all force vectors and find their sum

Practical Advice and Solution

  • The apple starts falling from the branch because of the wind gust and gravity pull it downwards.
  • You can find the magnitude and direction by summing the components of all force vectors
  • Another example is pulling his dog with force at an angle.
  • Force components are expressed as projections of the vector to the corresponding axes.

Newton’s Second Law

  • Object acceleration is directly proportional to the net force and inversely proportional to the object mass.
  • Formula: F=ma.

Newton’s Third Law

  • Whenever two physical objects interact, the magnitude of their forces are always equal but opposite.
  • Every action is going to have an opposite reaction

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Forces and The Laws of Motion - Physics

Description

Test your knowledge of forces and their effects on objects. This quiz covers types of forces, Newton's laws, friction, and inertia. It also includes questions on force calculations and free-body diagrams.

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