Projectile motion

4.5 Projectile Motion

Overview

  • Academic Year: 2025/2026

  • Content Title: Projectile Motion

  • Associated Teaching Program: 12 ATAR Physics

  • Curriculum Framework: SCSA Syllabus

Key Concepts

Understanding Projectile Motion
  • Projectile motion can be analyzed by treating the horizontal and vertical components of motion independently. This independence allows the application of kinematic equations:

    • Equations of Motion:

    • v=u+atv = u + at

    • s=ut+rac12at2s = ut + rac{1}{2}at^2

    • v2=u2+2asv^2 = u^2 + 2as

    • Average velocity: vav=racstv_{av} = rac{s}{t}

    • Kinetic energy: Ek=rac12mv2E_k = rac{1}{2}mv^2

Tasks and Investigations
  • Task 1 Lab: Investigation into Projectile Motion during Week 7.

  • Task 2 Lab: Investigation into Circular Motion in the Horizontal Plane during Week 9.

Circular Motion

  • An object with a net force of constant magnitude acting perpendicular to its motion experiences uniform circular motion.

  • In a horizontal circle, important formulas include:

    • Velocity: v = rac{2eta r}{T}

    • Centripetal acceleration: ac=racv2ra_c = rac{v^2}{r}

    • Resultant force: Fresultant=mimesac=racmv2rF_{resultant} = m imes a_c = rac{mv^2}{r}

Historical Context

Key Figures
  • Galileo Galilei: Important contributions include:

    • No horizontal force is involved post-initial thrust (i.e., momentum in horizontal direction is constant).

    • Vertical motion experiences acceleration due to gravity ( extit{g}).

    • Established independence of horizontal and vertical motions.

True or False Statements

Statements and Revisions
  1. A ball thrown directly upwards into the air has no net force acting on it during flight.

    • This is false due to gravitational force acting downwards.

  2. The path of a projectile with horizontal velocity is parabolic if air resistance is negligible.

    • True, under ideal conditions.

  3. Due to air resistance, the angle of descent of a projectile is always greater than the angle of projection.

    • True, air resistance alters the trajectory.

  4. The net force acting on a projectile at its apex is zero.

    • False; the force of gravity still acts.

Analysis Tools

Vector Representation
  • Draw vectors to illustrate understanding of projectile motion and the independence of components.

Worked Examples

Example 4.5.1: Horizontal Launch
  • Scenario: A golf ball of mass 153 g hits horizontally with speed 25.0 m/s from a height of 40.0 m. Ignore air resistance;

    • Use g=9.80extm/s2g = 9.80 ext{ m/s}^2.
      #### Calculations:

    1. Time taken to land (using vertical motion):

    • t=racextheightg=rac40.09.80t = rac{ ext{height}}{g} = rac{40.0}{9.80} (approx. 4.08 seconds)

    1. Horizontal distance traveled:

    • range=speedimestimerange = speed imes time

    • range=25.0extm/simestrange = 25.0 ext{ m/s} imes t

    1. Final velocity upon impact is calculated considering both components.

Example 4.5.2: Energy Considerations
  • Scenario: A ball of mass 535 g is thrown from a height of 1.50 m horizontally at 5.00 m/s; #### Calculations:

    • Apply work-energy principles to find the final velocity when landing.

Effects Influencing Projectile Motion

Air Resistance
  • Impact of Air Resistance:

    • Reduces calculated range and maximum height.

    • Affects trajectory by increasing the maximum angle during projection.

Angle and Range Relationship
  • Optimal Launch Angles:

    • Different angles result in distinct ranges:

    • 75°, 45°, 30°, and 15° have varied paths and distances for projectiles.

Problem-Solving Exercises

  1. A long jumper takes off at 8.25 m/s at 12.5°:

    • Calculate initial horizontal and vertical velocities through trigonometric decomposition using:

      • Horizontal component: vx=vimesextcos(heta)v_{x} = v imes ext{cos}( heta)

      • Vertical component: vy=vimesextsin(heta)v_{y} = v imes ext{sin}( heta)

  2. Analyze the trajectory of a projectile (an arrow or ball) to find velocity changes, maximum height, and landing distance.

Advanced Problems

  1. Determine the vertical take-off velocity and horizontal displacement in various projectile scenarios.

  2. Calculate time of flight, maximum height for projectile trajectories.

  3. Analyze angles and their respective effects on distance and height.

Caveats and Practical Considerations

Launch Angle Observations
  • It is often observed that launching at less than 45° maximizes range due to gravitational effects and air resistance considerations.

Velocity Impact Analysis
  • Conclusions can be drawn about velocity and acceleration based on the projectile’s height at various points in its trajectory.

Historical Insights on Projectile Dynamics
  • Referencing historical figures like Napoleon can elucidate principles of projectile range and impact concerning angle of launch.

Conclusion

  • Comprehensive understanding of projectile motion involves analyzing the independence of horizontal and vertical components and how various factors—like angle of launch, height, and air resistance—interplay to affect trajectory and impact.