تانية ثانوي أول محاضرة في الترم التاني كاملة 2026 الشغل

Name: تانية ثانوي أول محاضرة في الترم التاني كاملة 2026 الشغل
Uploaded: 2026-02-03T12:43:03.000Z
Duration: 4 h 10 min 11 s

Introduction to Work in Physics

Overview of the Lesson

The lesson begins with a greeting and an introduction to the topic of "work" from a physics perspective.

The instructor explains that standing still does not constitute work in physics, using the example of a person behind the camera who exerts no physical effort.

Understanding Work

Work is defined as the product of force and displacement; if there is no movement, no work is done, regardless of time spent.

The concept emphasizes that students studying hard may also be doing zero work physically since they are not moving objects.

Conditions for Work to Occur

Requirements for Physical Work

For work to occur, two conditions must be met: there must be a force applied and displacement in the direction of that force.

A metaphor involving a donkey pulling a cart illustrates how animals or people can exert force but may not always do significant work depending on their actions.

Example Analysis

The instructor discusses how increased load on a cart requires more force due to friction, demonstrating how both force and distance affect the amount of work done.

Calculating Work Done

Formula for Work

The formula for calculating work (W = F × d), where W is work, F is force in Newtons, and d is distance in meters.

An example calculation shows that if a donkey pulls 100 Newtons over 2000 meters, it performs 200,000 Joules of work.

Conditions Recap

Reiterates that physical work requires an effective force acting over a distance; without these elements, no work can be claimed.

Practical Application: Force Direction

Understanding Force Application

A practical demonstration involves pushing against an object while discussing how pressure relates to area when applying force.

Importance of Angle in Force Application

Discusses scenarios where forces are applied at angles and how this affects calculations regarding effective displacement versus total applied force.

Mathematical Concepts Related to Forces

Trigonometric Relationships

Introduces basic trigonometry concepts relevant to physics such as sine and cosine functions used for resolving forces into components based on angles.

Component Forces Explained

Explains how horizontal (adjacent side using cosine function) and vertical (opposite side using sine function) components relate back to overall applied forces.

Understanding Work and Force in Physics

The Relationship Between Pressure, Work, and Force

The discussion begins with calculating the pressure exerted by a force at an angle, emphasizing the importance of understanding both pressure and work.

The teacher highlights that work is defined as the product of force and the cosine of the angle between force and displacement, indicating a blend of concepts rather than separation.

A humorous interaction occurs regarding cooperation in moving a table, illustrating practical applications of physics principles in everyday life.

Techniques for Moving Objects

The instructor explains that pulling (as opposed to pushing) reduces friction on surfaces, making it easier to move heavy objects like tables.

Analyzing forces during pulling reveals that part of the applied force lifts the object slightly, reducing its weight on the surface and thus decreasing friction.

Practical Applications of Work

The conversation shifts to real-life implications: it's more efficient to pull rather than push heavy objects due to reduced frictional forces.

Students are prompted to recall the formula for work: W = F cdot d cdot cos(theta) , where F is force, d is displacement, and theta is the angle between them.

Factors Affecting Work Done

Key factors influencing work include magnitude of force, distance moved in direction of force, and angle between them; these relationships are crucial for understanding physical interactions.

Emphasis is placed on how changing angles affects work done; specifically noting that when angles approach 90 degrees or beyond, work can become negative or zero.

Understanding Units and Dimensions

Discussion transitions into units used in measuring work: Joules (J), which equate to Newton-meters (N·m).

Clarification on dimensional analysis shows that one Joule corresponds to one Newton acting over one meter. This reinforces foundational knowledge necessary for solving physics problems.

Work and Energy Concepts

Definition of Work

Work is defined as the amount of energy transferred when a force of 1 Newton moves an object 1 meter in the direction of the force, equating to 1 Joule.

Calculating Work with Different Forces

The work done by a force can also be calculated using different magnitudes; for example, a force of 5 Newtons moving an object 1 meter results in 5 Joules.

It is permissible to express work done by a force of 1 Newton moving an object over a distance of 5 meters.

Conditions for Positive Work

The formula for work (W = F * d * cos(θ)) indicates that work is positive when the cosine component is positive, which occurs when the angle θ between the force and displacement vectors is between 0° and less than 90°.

Specifically, if θ equals zero, then cos(θ) equals one, resulting in maximum positive work.

Examples and Applications

If an object experiences a force at an angle less than 90°, such as θ being greater than or equal to zero but less than 90°, then the cosine value remains positive.

Calculating Work with Angles

Example Calculation

An example involves applying a force of 50 Newtons on an object moving it through a distance of 30 meters at an angle of 60°. The calculation follows: W = F * d * cos(θ).

Substituting values gives W = (50 N)(30 m)(cos(60°)), leading to W = (50)(30)(0.5), resulting in total work done as 750 Joules.

Further Scenarios Involving Force and Motion

Additional Example Scenario

A scenario describes applying a force on an object with mass (50 kg), initiating movement from rest with uniform acceleration (2 m/s²).

Solving for Work Done

When calculating work while moving through various distances or time intervals, it's essential to apply appropriate formulas based on given conditions like direction and acceleration.

Understanding Motion Over Time

Movement Analysis Over Time

When analyzing motion over time (10 seconds), if movement occurs in the same direction as the applied force, calculations simplify due to direct alignment.

Using Kinematic Equations

To find displacement under constant acceleration from rest:

Initial velocity v_i : Zero,

Acceleration a : Two,

Time t : Ten seconds.

Displacement Calculation Methods

Various methods exist for calculating displacement:

Using average velocity,

Graphical representation under curves,

Applying kinematic equations directly.

Final Thoughts on Kinematics

Key Formulas Recap

Important kinematic equations include:

Displacement d = v_i t + 1/2at^2 ,

Average speed calculations,

Relationships between initial and final velocities under constant acceleration scenarios.

Understanding Motion Equations and Work

Motion Equations in Physics

The speaker discusses the removal of a section from the curriculum regarding motion equations with constant acceleration, emphasizing its importance in physics.

A relationship between velocity (v) and time (t) is established, where initial velocity (v₀) is not zero. The area under the graph represents distance.

The equation for distance (d = v₀ * t + 0.5 * a * t²) is highlighted as essential for solving various problems, regardless of whether they involve rest or not.

Understanding Forces and Work

The discussion shifts to when work done by a force is maximized; it occurs when the force direction aligns with displacement.

When discussing negative work, it's explained that this happens when the angle between force and displacement exceeds 90 degrees.

Examples are provided to illustrate scenarios where forces act against motion, such as driving uphill or applying brakes.

Practical Applications of Work Concepts

An example involving a rubber band illustrates how tension creates opposing forces during movement, affecting work calculations.

The distinction between work done by an individual versus external forces like gravity is emphasized through practical examples involving lifting weights.

Gravity's Role in Work Calculations

The speaker explains how gravitational force acts on objects being lifted, contrasting it with other forces acting on them during movement.

It’s noted that while gravity does negative work during ascent due to opposing directions, it does positive work during descent.

Key Insights on Zero Work Scenarios

A critical point made about conditions under which no work is done: specifically when the angle between force and displacement equals 90 degrees.

Further clarification on projectile motion indicates that gravitational influence changes depending on whether an object ascends or descends.

Understanding Work and Zero Work in Physics

Conditions for Zero Work

The concept of work being zero is introduced, particularly when force is zero or displacement occurs without applied force.

An example illustrates that pushing a stationary car (due to the handbrake) results in zero work despite exerting effort.

Pushing against a wall also yields zero work because there is no displacement; similarly, holding a heavy bag without moving results in zero work due to lack of movement.

Angle and Work Calculation

When the angle between the force and displacement is 90 degrees, such as gravity acting on a horizontally moving object, the work done by gravity is zero.

The electron orbiting around a nucleus does not do work since the angle between its instantaneous motion and the attractive force from the nucleus remains at 90 degrees.

Graphical Representation of Work

The relationship between force and displacement can be represented graphically; area under the curve represents total work done.

For positive values of force and displacement, calculating area gives positive work. However, if part of it falls into negative territory (like downward movement), it can result in net zero work.

Motion Characteristics Affecting Work

If an object's speed increases uniformly over time (positive acceleration), it indicates positive work being done. Conversely, if speed decreases uniformly (negative acceleration), negative work occurs.

On smooth surfaces with constant velocity, frictionless conditions lead to zero net work since no opposing forces act against motion.

Comparing Forces and Work Done

In scenarios where friction exists while pushing an object forward, different forces contribute to overall calculations of work done based on their angles relative to motion direction.

A comparison between two cars with different masses but equal accelerations shows that they require equal amounts of energy/work despite differing weights.

Practical Examples in Physics Problems

A problem involving two cars with different masses demonstrates how to calculate ratios based on their respective distances traveled under similar conditions.

Understanding that both vehicles are powered by engines helps clarify how external factors like friction influence total energy expenditure during movement.

This structured summary captures key concepts discussed regarding physics principles related to "work" while providing timestamps for easy reference back to specific parts of the transcript.

Understanding Work and Force in Physics

Key Concepts of Work

The lecture emphasizes that work is defined as the product of force and displacement, represented mathematically as W = F cdot d cdot cos(theta) .

It clarifies that the angle theta is between the direction of force and the direction of displacement, which affects the calculation of work done.

Important conditions for work:

Positive work occurs when theta < 90^circ .

Negative work occurs when theta > 90^circ.

Zero work happens when theta = 90^circ.

Calculating Work Done

The total work can be calculated by considering both applied forces and opposing forces like friction.

An example illustrates calculating work using a car being pushed with a force parallel to its movement.

Practical Examples

When pushing a car with a force of 100 N over a distance of 3 m, the total work done is calculated as W = F cdot d = 100N cdot 3m = 300J.

If the force applied is at an angle (e.g., 30 degrees), it requires resolving this into components to find effective force contributing to displacement.

Understanding Forces in Different Scenarios

When lifting an object vertically, such as raising a car, the weight acts downward while you apply an upward force equal to its weight.

The formula for gravitational potential energy (work done against gravity): W = F_g cdot h, where F_g = mg.

Special Cases in Work Calculation

If carrying an object horizontally while walking, no vertical displacement means zero work despite applying force.

In scenarios where motion opposes applied forces (like braking), negative work results from calculating using angles greater than 90 degrees.

Summary on Units and Dimensions

The unit for measuring work is Joules (J), equivalent to Newton-meters.

Clarification on dimensional analysis: Work dimensions are derived from mass times acceleration times distance ( kg·m^2/s^2).

This structured overview captures essential concepts discussed in the lecture regarding physics principles related to work and forces.

Understanding Work in Physics

Concepts of Work and Force

The concept of work in physics requires both a force and displacement caused by that force. The teacher illustrates this with an example involving a child named "Rafid."

A horizontal force of 100 Newtons acting on a small cart moving 10 meters east demonstrates how to calculate work done using the formula W = F cdot d cdot cos(theta) .

In another scenario, a 50 Newton force acts on an object moving 20 meters west, showcasing how direction affects work calculation.

Positive and Negative Work

When an object moves in the same direction as the applied force, the work done is positive; if it moves against the force, the work is negative.

The angle between the direction of motion and applied force determines whether work is positive or negative. For instance, at angles of 0° (positive), 180° (negative), or other values leading to zero work.

Conditions for Zero Work

Work can be zero if there’s no displacement despite applying a force. This occurs when surfaces are smooth or when speed remains constant without acceleration.

If friction exists on a rough surface while maintaining constant speed, forces may still act but do not result in net zero work due to opposing frictional forces.

Maximum Work Scenarios

Maximum work occurs when the angle between force and displacement is zero degrees ( cos(0°)=1).

Understanding cosine values helps determine conditions for maximum or minimum work based on angles like 60°, 90°, 180°, etc..

Practical Examples of Forces and Motion

An example discusses how braking forces exert negative work since they oppose vehicle motion.

Various scenarios illustrate different cases where forces act upon objects on smooth surfaces, emphasizing calculations involving cosine functions for determining effective forces.

Comparative Analysis of Different Cases

Comparing two bodies' movements shows how varying angles affect calculated works. The relationship between angles and resultant works highlights practical applications in physics.

Emphasizing that mass differences do not impact calculations as long as forces remain consistent across different scenarios.

This structured overview captures key insights from discussions about physical concepts related to work, providing clarity on fundamental principles through examples and calculations.

Work and Energy in Physics

Work Done by Gravity

The scenario describes a projectile motion where the work done is calculated using the formula W = F cdot cos(theta) cdot d . Here, with an angle of 60 degrees, the work results in 500 Joules.

In this phase, it is noted that when displacement is opposite to the force (gravity), the work done is negative. Conversely, if both force and displacement are in the same direction, as seen later, the work becomes positive.

Circular Motion and Work

During circular motion under centripetal force, it’s established that when the angle between force and displacement is 90 degrees, no work is done (work equals zero).

Examples illustrate scenarios where weight acts downward while movement occurs horizontally or vertically; these situations also yield zero work due to perpendicular forces.

Effects of Gravity on Movement

When considering a person descending from a height without frictional forces, gravity does positive work since its direction aligns with the movement.

The relationship between displacement and time for two bodies moving on a smooth surface indicates that body X moves at constant speed (zero acceleration), resulting in zero net work.

Acceleration and Work Relationships

Body Y experiences increasing difficulty as it climbs; thus it has positive acceleration leading to positive net work being done on it.

For different phases of motion analyzed through graphs:

Phase A shows positive acceleration leading to positive work.

Phase B indicates zero acceleration hence zero net work.

Analyzing Multiple Bodies

In analyzing three bodies on a smooth surface:

Body Z has zero acceleration indicating no net work.

Body X shows increasing speed implying positive net work due to increasing force.

The relationships among forces acting on bodies X and Y reveal that both experience varying amounts of net work based on their respective accelerations.

Graphical Representation of Work

A graph illustrates how total applied force relates to displacement. The slope represents F cdot cos(theta), allowing calculation of effective forces acting over distances traveled.

It’s concluded that if all forces act in alignment with displacement (cosine theta equals one), then maximum efficiency in energy transfer occurs across all bodies involved.

Comparative Analysis of Forces

Comparing forces acting on two bodies reveals differences based on angles relative to their displacements. This analysis helps determine which body experiences more significant effects from applied forces during motion.

By structuring notes this way with timestamps linked directly to specific insights within each section, readers can easily navigate through complex discussions about physics concepts related to energy and motion.

Work and Forces in Physics

Understanding Work Done by Forces

The relationship between weight and force is discussed, emphasizing that if speed increases, the force exceeds weight; if speed decreases, the force is less than weight. However, in this case, work is done equal to the weight of the body multiplied by height.

The work done by a force when lifting an object against gravity can be calculated using the formula: Work = Force × Height. Here, it’s noted that the acceleration due to gravity (g) plays a crucial role.

When two equal forces act on stationary bodies moving rightward, their net effect results in movement. The ratio of work done on both bodies during horizontal displacement is analyzed.

Friction and Net Force

If frictional forces are equal to applied forces, then net force equals zero. This leads to no movement; however, if one force is greater than another (e.g., friction), it affects motion significantly.

Calculating Work Done Over Time

A scenario involving a 2 kg mass subjected to a horizontal force of 10 N over four seconds illustrates how to calculate work done based on distance traveled and time taken.

To find acceleration from applied force divided by mass (F/m), further calculations lead to determining displacement using kinematic equations.

Displacement and Work Calculation

The area under a velocity-time graph represents displacement. For example, calculating displacement as half base times height gives insight into total distance covered during acceleration phases.

An example with a motorcycle's combined mass shows how net work can be calculated considering motor power versus frictional resistance over a specified distance.

Stages of Motion and Work Done

A person carrying a bag experiences different stages of motion: horizontal movement does not involve work while vertical ascent requires calculation based on gravitational potential energy changes.

Ascent involves calculating work against gravity using W = F × cos(θ). In contrast, descending involves negative work since gravitational pull acts downward while moving upward.

Energy Considerations in Circular Motion

Electrons do not perform work while orbiting nuclei because centripetal forces act perpendicular to their motion direction—resulting in zero net work due to cosine factors being zero at 90 degrees.

Similarly, planets do not exert or receive significant work during circular orbits around the sun for analogous reasons related to directional forces relative to motion paths.

Comparing Forces Across Different Bodies

When comparing two bodies affected by identical forces across smooth surfaces but taking different times for displacements reveals that ratios remain consistent due to uniformity in applied conditions.

Calculating Work Based on Angles

Relationship Between Force and Angle

The relationship between applied force magnitude (20 N), displacement (4 m), and angle θ indicates how these variables interact through trigonometric functions like cosine affecting total mechanical work output.

Specific angles yield varying amounts of effective work done; for instance, at 60 degrees or 90 degrees where cosine values change significantly impacting overall calculations for energy transfer efficiency.

Conceptual Questions Regarding Work

Why Do Electrons Not Do Work?

Electrons revolving around atomic nuclei do not perform any mechanical work due to constant perpendicular orientation of centripetal forces relative to their path—leading effectively towards zero energy expenditure despite continuous motion.

Planetary Motion Dynamics

Similar principles apply regarding planetary movements around stars where gravitational pulls maintain circular trajectories without performing substantial external mechanical works owing again primarily due directional alignments throughout orbital paths.

Understanding Work and Energy in Physics

Concepts of Displacement and Work

The relationship between displacement (d) and speed is discussed, illustrating how an increase in speed affects the distance covered over time. For example, if speed increases to 10 m/s, the new speed can reach up to 20 m/s.

The displacement increases fourfold due to the increased velocity, leading to a corresponding increase in work done by four times compared to the initial phase.

The discussion introduces two phases of motion: ascending and descending. During ascent, gravitational force does negative work while during descent it does positive work.

Calculating Work Done

The formula for calculating work (W = F * d * cos(θ)) is presented, emphasizing that work can be increased either by increasing force or adjusting the angle θ between force and displacement.

Two methods are proposed for increasing work over a distance of 1 meter:

Increasing the applied force (F).

Adjusting the angle θ to maximize cos(θ).

Analyzing Forces and Angles

A graphical representation shows two bodies affected by different resultant forces. It raises questions about determining angles based on these forces.

The tangent function is used to relate angles with forces acting on two different bodies. This leads into discussions about ratios of tangents corresponding to their respective forces.

Final Thoughts on Energy Concepts

Concluding remarks highlight calculations involving angles derived from tangent values related to forces acting on objects.

The session wraps up with encouragement for students as they transition into discussions about energy in future lectures.