IB Physics-Topic 2-2.1 -Motion

 

International-mindedness:

• International cooperation is needed for tracking shipping, land-based transport, aircraft and objects in space

Theory of knowledge:

• The independence of horizontal and vertical motion in projectile motion seems to be counter-intuitive. How do scientists work around their intuitions? How do scientists make use of their intuitions?

 

Application

  • Determining instantaneous and average values for velocity, speed and
    acceleration

  • Solving problems using equations of motion for uniform acceleration

  • Sketching and interpreting motion graphs

  • Determining the acceleration of free-fall experimentally

  • Analysing projectile motion, including the resolution of vertical and horizontal

    components of acceleration, velocity and displacement

  • Qualitatively describing the effect of fluid resistance on falling objects or
    projectiles, including reaching terminal speed

Utilization
  • Diving, parachuting and similar activities where fluid resistance affects motion

  • The accurate use of ballistics requires careful analysis

  • Biomechanics (see Sports, exercise and health science SL sub-topic 4.3)

  • Quadratic functions (see Mathematics HL sub-topic 2.6; Mathematics SL sub-topic 2.4; Mathematical studies SL sub-topic 6.3)

  • The kinematic equations are treated in calculus form in Mathematics HL sub-topic 6.6 and Mathematics SL sub-topic 6.6

Understanding

  • Distance and displacement

  • Speed and velocity

  • Acceleration

  • Graphs describing motion

  • Equations of motion for uniform acceleration

  • Projectile motion

  • Fluid resistance and terminal speed

Distance and displacement

Speed and velocity

This text is for illustrative purposes only. What you're reading here is sample text.

Acceleration

This text is for illustrative purposes only. What you're reading here is sample text.

This text is for illustrative purposes only. What you're reading here is sample text.

  • Distance and displacement

DistanceDisplacementScalarVectorA scalar quantity which measures how far two locations are apart from each other along a certain path.A vector quantity defined by the length and direction of the line segment joining the initial and final positions of an object.

 

 

  • Speed and velocity

SpeedVelocityScalarVectorRate of change of distance to time.Rate of change of displacement to time.

Velocity is a measure dependent on the motion of the observer. The relative velocity of A to B is equal to the vector subtraction of the velocity of B from the velocity of A.

  • Acceleration

AccelerationVectorRate of change of velocity,Acceleration due to gravity of any free-falling object is given by g=9.81m/s^2. This value does not depend on the mass of the object.

Take note that acceleration is a vector and thus has a direction. If we assume the upwards direction to be positive, the acceleration due to gravity would have a negative value of g=-9.81m/s^2.

  • Graphs describing motion

Displacement-time graph

 

The slope gradient indicates the velocity.

Straight lines imply constant velocity.

Velocity-time graph

 

The slope gradient indicates the acceleration.

Straight slanted lines imply constant acceleration or deceleration.

The area under the lines indicates the change in displacement.

Acceleration-time graph

 

Horizontal lines imply constant acceleration.

The area under the lines indicates the change in velocity.

 

  • Fluid resistance and terminal speed

Air resistance limits the maximum velocity an object could attain from free-falling. For example:

  • If you jump out of a plane and undergo free-falling, you will feel an upward force exerted on you by the surrounding air due to air resistance.
  • As you fall faster and faster due to gravity, this upward force exerted by air becomes greater and greater until it balances your weight. At this point, the net force acting on you becomes zero, and you no longer accelerate.
  • This specific velocity at which you stop accelerating during a free-fall is called the terminal velocit

  • Projectile motion

An object is said to undergo projectile motion when it follows a curved path due to the influence of gravity.

If we assume air resistance to be negligible in a projectile motion:

  • The horizontal component of velocity is constant
  • The vertical component of velocity accelerates downwards at 9.81m/s^2
  • The projectile reaches its maximum height when its vertical velocity is zero
  • The trajectory is symmetric

 

The presence of air resistance changes the trajectory of the projectile by the following

  • The maximum height of the projectile is lower
  • The range of the projectile is shorter
  • The trajectory is not symmetric