Physics Chapter 13: Forces
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Questions and Answers

What is a force?

A force is a push or pull that causes an object to move, stop, or change direction. Or anything that makes an object accelerate.

How is the strength of a force measured?

The strength of a force is measured in the SI unit called the newton (N) and is measured by using a spring balance.

Which of the following is NOT a type of force?

  • Sound force (correct)
  • Friction force
  • Electric force
  • Gravity force
  • Applied force
  • Spring force
  • Drag force
  • Normal force
  • Magnetic force

What is the difference between mass and weight?

<p>Mass is the amount of matter in an object, measured in grams (g) or kilograms (kg). Weight is the pull of gravity on an object, measured in newtons (N).</p> Signup and view all the answers

What is the formula for calculating weight?

<p>W = mg</p> Signup and view all the answers

If the mass of an object is 74 kg, what is its weight?

<p>740 N</p> Signup and view all the answers

If the mass of an object is 800 grams, what is its weight?

<p>8 N</p> Signup and view all the answers

If the weight of an object is 560 N, calculate its mass in kilograms.

<p>56 kg</p> Signup and view all the answers

What is meant by air resistance?

<p>Air resistance, also known as drag, is a kind of friction (a force that opposes motion) that occurs between air and another object. It's the force an object encounters as it moves through the air.</p> Signup and view all the answers

What is upthrust?

<p>Upthrust is a force that only exists in liquids. It's a push that always goes straight up, against the direction of gravity.</p> Signup and view all the answers

Why does a boat float?

<p>A boat floats because the upward force of upthrust from the water balances the downward force of gravity acting on the boat. When forces are balanced, there is no net force, and the boat remains at rest.</p> Signup and view all the answers

What would happen if the forces acting on the boat were not balanced?

<p>If the forces were not balanced, the boat would either sink or be pushed upwards. If the downward force of gravity is stronger than the upward force of upthrust, the boat would sink.</p> Signup and view all the answers

What is friction?

<p>Friction is a common force that tries to stop movement between touching surfaces. It's caused by roughness between the surfaces, creating resistance to movement.</p> Signup and view all the answers

Friction is always a disadvantage.

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

Forces always come in pairs.

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

Forces can be described by magnitude and direction only.

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

Balanced forces cause a change in motion.

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

If two forces, one of 10N to the right, and another of 4N to the left, act on an object, what is the net force and its direction?

<p>The net force is 6N to the right.</p> Signup and view all the answers

The unit for moment is Nm.

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

What are the two types of moments?

<p>The two types of moments are clockwise and anticlockwise.</p> Signup and view all the answers

What is the principle of moment?

<p>The principle of moment states that an object is balanced when the clockwise moment is equal to the anticlockwise moment.</p> Signup and view all the answers

How does the force applied affect the moment?

<p>The greater the force applied, the greater the moment.</p> Signup and view all the answers

How does the distance from the pivot affect the moment?

<p>The greater the distance from the pivot, the greater the moment.</p> Signup and view all the answers

What is volume?

<p>The amount of space an object occupies (C)</p> Signup and view all the answers

What is density?

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

What are the units for density?

<p>The units for density are typically g/cm³ or kg/m³.</p> Signup and view all the answers

What is the formula for calculating mass?

<p>Mass = density x volume</p> Signup and view all the answers

What is the formula for calculating volume?

<p>Volume = mass/density</p> Signup and view all the answers

An object is made from steel. It has a volume of 25 meter cube and a mass of 425 kg. Calculate the density of the object.

<p>17 kg/m³</p> Signup and view all the answers

An object has a volume of 0.004 meter cube and a density of 980kg/meter cube. Calculate the mass.

<p>3.92 kg</p> Signup and view all the answers

A bottle of water has a density of 1000kg/m³ and a mass of 0.5 kg. Calculate the volume of the water bottle.

<p>0.0005 m³</p> Signup and view all the answers

An object has a mass of 5 kg and a density of 2 g/cm³. Calculate the volume of the object.

<p>2500 cm³</p> Signup and view all the answers

What is pressure?

<p>Pressure is defined as the force per unit area.</p> Signup and view all the answers

What is the formula for calculating pressure?

<p>Pressure = Force/Area</p> Signup and view all the answers

The SI units for pressure are N/m², N/cm², or Pascal (Pa).

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

A force of 800 N acts on an area of 200 square meters. Calculate the pressure.

<p>4 N/m²</p> Signup and view all the answers

A crate exerts a force of 120 N on a table. The pressure on the table is 15 N/m². Calculate the area of the crate that is in contact with the table.

<p>8 m²</p> Signup and view all the answers

In simple terms, how does the force affect pressure?

<p>Increasing the force on a specific area increases the pressure.</p> Signup and view all the answers

How does the area affect pressure?

<p>Decreasing the area over which the force is applied increases the pressure.</p> Signup and view all the answers

Why does a person wearing high heels exert more pressure on the ground compared to someone wearing sneakers?

<p>The area of contact with the ground is smaller for high heels compared to sneakers. The same force applied over a smaller area results in higher pressure.</p> Signup and view all the answers

Pressure in liquids is transmitted in all directions equally.

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

The pressure in liquids is independent of the shape and size of the container.

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

The pressure in a liquid is directly proportional to its depth.

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

How does the motion of gas molecules contribute to pressure?

<p>Gas molecules are constantly moving and colliding with the walls of their container. These collisions exert force on the walls and cause a pressure, known as gas pressure.</p> Signup and view all the answers

Which of the following is NOT a feature of air pressure?

<p>Is the same at all locations on Earth (B)</p> Signup and view all the answers

Flashcards

What is a force?

A push or pull that causes an object to move, stop, or change direction.

What is mass?

The amount of matter in an object. It is measured in grams (g) or kilograms (kg).

What is weight?

The pull of gravity on an object. It is a type of force. It is measured in Newtons (N).

What is a Newton (N)?

The SI unit for measuring force. It is named after the English scientist Sir Isaac Newton.

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What is air resistance?

A type of friction that occurs between air and an object as it moves through the air.

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What is upthrust?

A force that exists only in liquids, pushing objects upwards against gravity.

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What is friction?

A force that opposes motion between two surfaces in contact.

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What are balanced forces?

Forces that cause no change in motion because they are equal in size and opposite in direction.

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What are unbalanced forces?

Forces that cause a change in motion because they are unequal in size or direction.

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What is net force?

The overall force acting on an object when unbalanced forces are present.

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What is a clockwise moment?

A force that causes an object to turn in a clockwise direction. It is calculated as force multiplied by distance.

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What is an anti-clockwise moment?

A force that causes an object to turn in an anti-clockwise direction. It is calculated as force multiplied by distance.

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What is the principle of moments?

The principle that for an object to be in equilibrium, the sum of clockwise moments must equal the sum of anticlockwise moments.

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What is volume?

The amount of space an object occupies. It is measured in cubic units, like cubic meters (m3) or cubic centimeters (cm3).

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What is density?

The measure of how much mass is contained in a given volume. It is calculated as mass divided by volume. Units are g/cm3 or kg/m3.

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What is pressure?

The force per unit area. It is calculated as force divided by area. Units are N/m2 or Pascal (Pa).

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What are the properties of pressure in liquids?

Pressure in liquids is transmitted equally in all directions. It increases with depth. It does not depend on the shape or size of the container.

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What are the properties of pressure in gases?

Pressure in gases is also transmitted equally in all directions. It is affected by factors like temperature and volume.

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What is atmospheric pressure?

The pressure that is exerted by the weight of the atmosphere. It decreases with altitude.

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What is fluid resistance?

The force that opposes the motion of an object through a liquid.

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What is a spring balance?

A tool used to measure the force exerted by an object. It typically consists of a spring attached to a scale.

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What is a balance scale?

A tool used to measure the mass of an object. It works by comparing the object's mass to a known standard mass.

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What is resultant force?

The difference between the forces acting on an object.

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What is the formula for calculating a moment?

The force applied multiplied by the perpendicular distance from the point of application of force to the axis of rotation.

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What is centripetal force?

A force that acts perpendicular to the surface and causes an object to move in a circular path.

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What is normal force?

A force that is always perpendicular to the surface and opposes motion.

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What is fluid pressure?

The pressure exerted by a fluid at a particular point.

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What is hydrostatic pressure?

The pressure that is exerted by a fluid due to its weight.

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What is a pressure gauge?

A device used to measure pressure. It typically uses a fluid to determine the pressure applied on a surface.

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What is the pressure-depth relationship?

The relationship between pressure and depth, where pressure increases linearly with depth.

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What is tension?

A force that is perpendicular to a surface and opposes motion.

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What is Boyle's law?

The relationship between pressure and volume, where pressure decreases as volume increases.

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Study Notes

Chapter 13: Forces

  • This chapter covers forces, types of forces, effects of balanced and unbalanced forces, turning forces, mass, volume, density, weight, pressure, and calculations.

What is a Force?

  • A force is a push or pull that causes an object to move, stop, or change direction.
  • In physics, a force is anything that makes an object accelerate.
  • Force is measured in Newtons (N).
  • Force can be measured using a spring balance.

Types of Forces

  • Friction force
  • Gravity force
  • Applied force
  • Drag force
  • Normal force
  • Magnetic force
  • Electric force
  • Spring force

Mass and Weight

  • Mass is the amount of matter in an object. Measured in grams (g) or kilograms (kg).
  • Weight is the pull of gravity on an object. It is a type of force measured in Newtons (N).
  • Weight can be measured using a spring balance.
  • Weight = mass x gravitational field strength (W = mg)

Calculations

  • Example 1: If mass = 74 kg, weight = 740 N ( using W = mg and g=10 N/kg)
  • Example 2: If mass = 800 g, weight = 8 N
  • Example 3: If weight= 560 N, mass=56 kg
  • Example 4: Worked example calculating the value of d, given the forces and distances of an object.

Air Resistance (Drag)

  • Air resistance is a form of friction that opposes motion between air and another object.
  • It's a force experienced by objects moving through the air.
  • Air resistance and gravity are two key forces on Earth.

Upthrust

  • Upthrust is a force that only exists in liquids (water, lakes, oceans, swimming pools, cups of tea etc.).
  • Upthrust is always a push straight up, against the direction of gravity.
  • Upthrust is the force that pushes objects up (buoyancy).

Balanced and unbalanced Forces

  • Forces occur in pairs and can be balanced or unbalanced.
  • Balanced forces do not cause a change in motion.
  • Unbalanced forces always cause a change in motion.
  • Unbalanced forces lead to a change in speed or direction.
  • Resultant force also called net force is the difference between the two forces and the direction is that of the largest force.
  • Examples of balanced forces: Example 1- if thrust and air resistance are equal then the force is balanced and the boat will not accelerate or decelerate in motion.
  • Examples of unbalanced forces example 1 - if thrust is greater than drag the object will accelerate in a direction of the largest force. Example 2 if the downward force (weight) is greater than the upward force (upthrust) the object will accelerate downwards.

Moments

  • Moment is a measure of turning effect of a force.
  • Moment = Force x perpendicular distance from the pivot.
  • Clockwise and anticlockwise moments.
  • Principle of Moments: For a balanced object, total clockwise moment = total anticlockwise moment.
  • Example calculations involving moments.

Mass, Volume and Density

  • Mass - The amount of matter in an object.

  • Volume - The amount of space an object occupies.

  • Density - The ratio of mass to volume (Density = mass/volume).

  • Units for density include g/cm³ or Kg/m³.

  • Example Calculations: Density, Mass, and volume.

Pressure

  • Pressure is defined as force per unit area (Pressure = Force/Area).

  • S.I Units for pressure include N/m² or N/cm² or Pascal (Pa).

  • Pressure in liquids acts in all directions. Pressure increases with depth

  • Example Calculations Pressure, Area, Force.

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Description

Explore the fundamental concepts of forces in this quiz covering types of forces, mass, weight, and related calculations. Understand the differences between balanced and unbalanced forces and their effects. Test your knowledge on how these principles apply to the physical world.

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