Dynamics and Forces Quiz

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Questions and Answers

What is the SI unit used to measure force?

Pascal (Pa)

Meter (m)

Newton (N) (correct)

Kilogram (kg)

How is weight determined for an object on Earth?

By using the formula $W = F/m$ where $F$ is the frictional force.

By using the formula $W = mg$ where $g$ is the speed of light.

By calculating the mass and multiplying by gravitational potential energy.

By using the formula $W = mg$ where $g$ is the acceleration of free fall. (correct)

What type of force is friction?

A gravitational force acting on an object.

A force acting in the same direction as the motion.

An upward buoyancy force in a fluid.

A force that arises when two surfaces rub against each other. (correct)

What does the formula $F = ma$ represent?

The relationship between force, mass, and acceleration. Signup and view all the answers

Which of the following correctly describes free-body diagrams?

They model all forces acting on an object with vectors and labels. Signup and view all the answers

In a fluid, what is the buoyant force acting upon an object called?

Up-thrust Signup and view all the answers

If a force results in constant acceleration, what must be true about the force acting on the object?

It must be constant. Signup and view all the answers

What effect does changing the location of an object (e.g., from Earth to the moon) have on its weight?

It decreases due to reduced gravitational force. Signup and view all the answers

What forces act on an object on a slope?

Weight, normal reaction force, and frictional force Signup and view all the answers

How is drag force related to the speed of an object?

It is proportional to the square of the speed Signup and view all the answers

What happens to an object in free fall once it reaches terminal velocity?

It stops accelerating and falls at a constant speed Signup and view all the answers

Which factor does NOT significantly influence the magnitude of drag force?

Color of the object Signup and view all the answers

What is the effect of increasing the cross-sectional area of a falling object in fluid?

It increases the drag force Signup and view all the answers

In which scenario will an object's acceleration reduce to zero?

When the net force acting on the object is zero Signup and view all the answers

Which statement about terminal velocity is false?

Terminal velocity increases with decreasing mass Signup and view all the answers

How can terminal velocity be experimentally determined for an object?

By measuring the time until acceleration becomes constant Signup and view all the answers

What is the unit of pressure that measures force per unit area?

Pascal (Pa) Signup and view all the answers

Using the formula $p = h \rho g$, what does the variable $h$ represent?

Height of the fluid column Signup and view all the answers

According to Archimedes' principle, what condition must be true for an object to float?

The upthrust is equal to the object's weight. Signup and view all the answers

What forces act on an object submerged in a fluid?

Both weight and upthrust forces Signup and view all the answers

Why does pressure at the base of a column of fluid remain uniform in all directions?

Due to the weight of the fluid above. Signup and view all the answers

What is the significance of the centre of mass in relation to motion?

It is the point where an external force causes linear motion only. Signup and view all the answers

Which method can be used to find the volume of an irregular solid?

Submerging the solid in water and measuring the change in water level. Signup and view all the answers

For a body to be in equilibrium, what must be true about the net forces acting upon it?

The net force in both the horizontal and vertical directions must be zero. Signup and view all the answers

What does the equation for pressure represent?

The normal force exerted on a surface divided by the area of that surface. Signup and view all the answers

How can the centre of mass of an object be determined using a plumb line?

By observing the intersection of lines drawn from two suspension points. Signup and view all the answers

In the context of equilibrium, what is a triangle of forces used for?

To visualize the resultant force acting on an object. Signup and view all the answers

What is the SI unit of density?

kg/m³ Signup and view all the answers

What is the formula to calculate density?

Density = Mass / Volume Signup and view all the answers

What must be true about the motion of a ball bearing once it reaches terminal velocity in a fluid?

The distance traveled in equal time intervals is constant. Signup and view all the answers

How is the moment of a force defined?

Magnitude of the force multiplied by the perpendicular distance. Signup and view all the answers

What is a couple in the context of rotational forces?

A pair of forces of equal magnitude in opposite directions. Signup and view all the answers

What condition defines a body in equilibrium regarding moments?

The sum of clockwise moments equals the sum of anti-clockwise moments. Signup and view all the answers

What is the SI unit for measuring the moment of a force?

Newton-meter (Nm) Signup and view all the answers

What happens if a force is applied parallel to the pivot?

It does not produce a moment. Signup and view all the answers

How can the torque of a couple be calculated?

By taking the product of one force's magnitude and the perpendicular separation. Signup and view all the answers

Which statement is true about terminal velocity?

It involves a balance of forces acting on the object. Signup and view all the answers

Study Notes

Dynamics

Force: A resultant force acting on a body with mass causes acceleration.
Force formula: F = ma (Force = mass × acceleration)
Newton: The SI unit of force, defined as the force that accelerates 1 kg by 1 m/s².
Weight: The gravitational force acting on an object, calculated as W = mg (Weight = mass × acceleration due to gravity).

Common Forces

Weight: The gravitational force acting on an object through its center of mass.
Friction: Resistive force arising when two surfaces rub against each other.
Drag: Resistive force on an object moving through a fluid (e.g., air or water).
Tension: Force within a stretched cable or rope.
Upthrust: Upward buoyancy force acting on an object in a fluid.
Normal Contact Force: Force acting at 90° to the plane when an object rests against another.

Free-Body Diagrams

Model forces acting on an object with vector arrows scaled to their magnitudes and directions.
Label each arrow with the force it represents.
Used to identify forces in planes and resolve net force in a specific direction.

Motion under Constant Force

Constant net force results in constant acceleration (F = ma).
Applies to motion on slopes, where forces are resolved parallel and perpendicular to the slope.

Non-Uniform Acceleration: Drag

Drag is a frictional force opposing motion through a fluid (air resistance).
Factors influencing drag include:
- Speed of the object.
- Object's shape and texture.
- Fluid density.
- Drag increases with the square of speed and cross-sectional area.

Terminal Velocity

Drag force increases with velocity during free fall, reducing net force and acceleration.
Terminal velocity is reached when drag force equals weight, resulting in zero net force and constant velocity.

Determining Terminal Velocity

Experimentally:
- Drop a ball bearing in viscous fluid, measuring the distance traveled at equal time intervals.
- Use a ticker timer to mark a tape attached to the ball bearing, analyzing dot spacing.
- Measure the distance traveled between dots, determine terminal velocity using time interval.

Equilibrium

Moment of a force: The turning effect of a force around a pivot point, M = Fd (Moment = Force × perpendicular distance).
Couple: A pair of equal magnitude, opposite direction forces acting in parallel, producing rotation without translation.
Torque: Product of one force's magnitude and perpendicular distance between forces, equaling the total moment of the couple.

Principle of Moments

In equilibrium:
- Net force is zero.
- Net moment is zero.
Sum of clockwise moments equals the sum of anti-clockwise moments about the same point.

Center of Mass and Center of Gravity

Center of mass: The point where an object's weight appears to act.
Center of gravity: Coincides with center of mass when the object is in a uniform gravitational field.
A freely suspended object comes to rest with its center of mass below the suspension point.

Density and Pressure

Density: Mass per unit volume, ρ = m/V (Density = mass / volume).
Pressure: Force per unit area, p = F/A (Pressure = force / area).
Pressure in a fluid: p = hρg (Pressure = height of fluid column × density × acceleration due to gravity).

Archimedes' Principle

Upthrust: Upward force acting on an object submerged in a fluid.
Archimedes' Principle states that the upthrust on an object is equal to the weight of the fluid displaced by the object.
An object sinks if upthrust is less than its weight.
A floating object has its weight equal to the weight of the fluid it displaces.

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Description

Test your knowledge on the principles of dynamics and various forces acting on objects. This quiz covers key concepts like force, weight, friction, and free-body diagrams. Challenge yourself to understand how these forces interact in the physical world.