Chapter 5 #2

Question 1

What defines the presence of a gravitational force on a mass?

Answer 1

A gravitational attractive (pulling) force exists on a mass if it is situated within a gravitational field created by another object possessing a huge mass, such as the Earth.

Question 2

What force is exerted on all masses due to the Earth’s gravitational field, and how is it directed?

Answer 2

All masses experience a force of attraction towards the center of the Earth, which is defined as weight.

Question 3

How is weight (W) calculated in terms of mass and gravitational acceleration?

Answer 3

Weight (W) is calculated as the product of mass (m) and gravity acceleration (g): W = m \times g.

Question 4

What is the primary definition of mass?

Answer 4

Mass is defined as the amount of matter contained within an object.

Question 5

How is inertial mass defined?

Answer 5

Inertial mass is the property of an object that resists any change in its state of motion.

Question 6

What is the definition of weight?

Answer 6

Weight is the force exerted on a mass specifically due to gravity.

Question 7

Is mass a scalar or vector quantity?

Answer 7

Mass is a scalar quantity.

Question 8

Is weight a scalar or vector quantity?

Answer 8

Weight is a vector quantity.

Question 9

What instruments are used to measure mass?

Answer 9

Mass is measured using a Top-pan balance or a Sensitive balance.

Question 10

What instrument is used to measure weight (or force)?

Answer 10

Weight is measured using a Spring balance, also known as a Force meter or Newton meter.

Question 11

What determines the value of a body’s mass?

Answer 11

The value of a body’s mass is constant, regardless of location.

Question 12

What determines the value of a body’s weight?

Answer 12

The value of a body’s weight changes depending on the place where it is measured (e.g., Earth, moon, etc.).

Question 13

What are contact forces?

Answer 13

Contact forces are forces that exist between bodies that are physically touching each other.

Question 14

Describe the normal contact force (or normal reaction, R or N) in the context of a body resting on a plane.

Answer 14

When a body is placed on a fixed plane, it pushes the plane down with a contact force equal to its weight. According to Newton’s third law, the plane pushes the body up with an equal contact force, called the normal contact force or normal reaction.

Question 15

What is the specific direction of the normal contact force relative to the surface?

Answer 15

The normal contact force always acts normally (perpendicular) to the surface, and not necessarily downwards.

Question 16

Define friction contact forces.

Answer 16

Friction is the force that acts to try and stop materials from sliding across each other.

Question 17

What is fluid friction, or drag force?

Answer 17

Fluid friction (or drag force) is the friction that exists between a body and any surrounding fluid (liquid or gas).

Question 18

Explain what causes fluid friction within a fluid itself.

Answer 18

Fluid friction exists between layers of a fluid that are moving at different speeds.

Question 19

Define viscosity.

Answer 19

Viscosity is a measure of a fluid’s resistance to flow, which can be thought of as a measure of how “sticky” the fluid is.

Question 20

Give an example illustrating the relationship between viscosity and drag force.

Answer 20

Honey is more viscous than water; therefore, an object moving through honey experiences a stronger drag force than an object moving through water.

Question 21

How does the speed of an object moving through a fluid relate to the drag force opposing its motion?

Answer 21

The faster an object moves through a fluid, the stronger the force of drag that opposes its motion.

Question 22

What is the common term for the fluid resistance of the atmosphere?

Answer 22

The fluid resistance of the atmosphere is commonly referred to as air resistance.

Question 23

How does air resistance change as an object falls through the air?

Answer 23

Air resistance opposes the object’s motion and increases as the object’s speed increases.

Question 24

What is the definition of density?

Answer 24

Density is mass per unit volume.

Question 25

State the formula for density (\rho).

Answer 25

Density is calculated as \rho = m/v, where m is mass and v is volume.

Question 26

What is the kinetic theory of matter?

Answer 26

The kinetic theory of matter is based on the idea that all matter is composed of particles that are in continual motion.

Question 27

At what temperatures does the continual motion of particles in matter exist?

Answer 27

This motion exists at all temperatures above absolute zero (i.e., Zero Kelvin).

Question 28

What is the fundamental observation that supports the kinetic model of gases?

Answer 28

The kinetic model is based on Brownian motion observations, which suggest that gas molecules are in a state of continual random motion.

Question 29

Describe the nature of collisions between molecules in the kinetic model of gases.

Answer 29

Molecules collide elastically, meaning there is no loss of total kinetic energy, with one another and with the container walls.

Question 30

According to the kinetic theory, what causes a gas to exert pressure on the container walls?

Answer 30

Pressure is caused by the random bombardment of gas molecules on the walls of the container.

Question 31

Why does the bombardment of gas molecules create a force on the container walls?

Answer 31

A force is exerted on the walls because there is a change in the momentum of the gas molecules during the collisions.

Question 32

Define pressure.

Answer 32

Pressure is defined as the force per unit area over which that force is distributed.

Question 33

What is upthrust, or buoyant force?

Answer 33

Upthrust is the upward force that a liquid or gas (fluid) exerts on a body that is partially or fully submerged in it; it is also known as buoyancy.

Question 34

Why does upthrust exist?

Answer 34

Upthrust exists because the pressure of the fluid on the bottom surface of the submerged body is greater than the pressure at the top surface.

Question 35

State the formula for pressure (P) at a depth h beneath the surface of a liquid.

Answer 35

Pressure is given by P = \rho gh, where \rho is the density of the fluid, g is the acceleration of freefall, and h is the depth.

Question 36

If the upthrust on a body is greater than the body's weight, what happens?

Answer 36

If the upthrust is greater than the weight of the body, the body accelerates upwards and rises.

Question 37

What does Archimedes' principle state regarding upthrust?

Answer 37

Archimedes' principle states that the upthrust is equal to the weight of the liquid displaced by the submerged object.

Question 38

State the formula for the Upthrust force (F_u).

Answer 38

The Upthrust force is calculated as F_u = \rho gV, where \rho is the density of the fluid, g is the acceleration of freefall, and V is the volume of the fluid displaced (or volume submerged).

Question 39

For a body moving through a liquid at constant velocity, what is the required condition for the forces?

Answer 39

Since the velocity is constant, the forces must be balanced (no resultant force), meaning Weight = Viscous Drag + Upthrust.

Question 40

In the case of a crane lifting a load at a uniform velocity, how does the tension (T) in the cable relate to the weight (W) of the load?

Answer 40

If the load is moving at a uniform velocity (or at rest), the net force is zero, so the tension equals the weight: T = W.

Question 41

If a crane is accelerating a load upwards, how is the tension (T) calculated?

Answer 41

The tension is T = m(g+a), where T > W.

Question 42

If a crane is accelerating a load downwards, how is the tension (T) calculated?

Answer 42

The tension is T = m(g-a), where W > T.

Question 43

When a person is standing in a lift, which force represents the force of the floor on the person?

Answer 43

The normal reaction (R), or normal push, of the floor on the person.

Question 44

When a person is accelerating inside a lift, is the normal reaction (R) necessarily equal to their weight (W)?

Answer 44

No, R is not necessarily equal to W. R represents the person's apparent weight and changes based on the lift's acceleration.

Question 45

Name the three forces acting on a body sliding down an inclined plane.

Answer 45

The three forces are the weight (W), the normal reaction (R), and the frictional force (F).

Question 46

State the formula for the normal reaction (R) on a body resting on an inclined plane with angle \theta.

Answer 46

The normal reaction is given by R = mg \cos\theta.

Question 47

State the general equation of motion for a body of mass m accelerating down an inclined plane with angle \theta and friction F.

Answer 47

The equation of motion is mg \sin\theta - F = ma.

Question 48

If an inclined plane is perfectly smooth (F=0), what is the acceleration (a) of the body sliding down the plane?

Answer 48

If the plane is smooth, the acceleration is a = g \sin\theta.

Question 49

When two bodies are connected by a single string and are moving, how do their accelerations compare?

Answer 49

Their accelerations must be equal in magnitude because they are physically connected.

Question 50

When two bodies are connected by a single string, how does the tension compare at both ends?

Answer 50

The tension (T) is equal at both ends of the string.

Question 51

Define the center of gravity.

Answer 51

The center of gravity is the point where all the weight of the object is considered to act.

Question 52

Define the moment of a force about a point.

Answer 52

The moment of a force about a point is the product of the magnitude of the force and the perpendicular distance from the pivot.

Question 53

State the principle of moments for an object in rotational equilibrium.

Answer 53

The principle of moments states that the sum of clockwise moments must equal the sum of anti-clockwise moments about the same pivot point.

Question 54

Define the torque of a couple.

Answer 54

The torque of a couple is the turning effect produced by two forces that are equal in magnitude, opposite in direction, and not acting along the same line.

Question 55

What are the necessary conditions for a body to be in equilibrium?

Answer 55

A body is in equilibrium if the net force acting on it is zero AND the net torque acting on it is zero.

Question 56

What energy transfer occurs when an object is submerged in a liquid?

Answer 56

When an object is submerged, the liquid gains GPE (displaced upward), and the object itself loses GPE.

Question 57

When two immiscible liquids are placed over each other in a container, how is the total pressure on the base calculated?

Answer 57

The total pressure on the base is the sum of the pressures due to the height of the first liquid layer and the height of the second liquid layer.

Question 58

In the formula F_u = \rho gV for upthrust, which density (\rho) must be used?

Answer 58

The density (\rho) used in the upthrust calculation must be the density of the liquid, not the density of the submerged object.

Question 59

How does density change with height in compressible fluids like atmospheric air?

Answer 59

Density decreases as height increases (or increases with depth) because the depth of the air column decreases.

Question 60

To determine the moment of a force, what component of the force must be used?

Answer 60

One must use the component of the force that is perpendicular to the distance from the pivot.

Question 61

For an object with the same density, how does doubling the mass affect the volume?

Answer 61

Given the same density, twice the mass means twice the volume.