B2.2.1 Fluid mechanics

Projectile motion

• Projectile: Refers to the motion of an object that has been projected into the air or dropped, and where the only forces acting on it are gravity and air resistance

• Centre of mass: the [mathematical] point around which the mass of a body or object is evenly distributed

Factors that affect projectile motion

• The pathway of the projectile and the overall distance travelled (range) depend on:

  • Initial conditions of projection:

    • initial velocity

    • angle of projection

    • height of release

  • air resistance

  • mass

Angle of projection

• The angle of projection is most significant for the maximum height of the flight and accuracy

• Long jump: the ideal takeoff angle is usually around 18-22 degrees, as too steep an angle reduces horizontal distance, while too shallow limits height

• 30 angle: the object will travel a moderate distance, focusing on horizontal momentum

• 45 angle: results in greater distance as it provides an optimal balance between vertical/horizontal components of motion

• 60 angle: object will achieve more height, but shorter horizontal distance, as much of the force is directed upward rather than forward

Height of release

• The higher the height of projection, the longer the range

• Javelin: Taller athletes or those with a higher release point can achieve greater distances due to the increased initial height

• Long jump: jumpers aim to jump upward as they reach the takeoff board, maximising their height at takeoff to increase hang time

Air resistance

• Faster-moving objects experience more air resistance, which means that air resistance is more of a factor for projectiles moving quickly than for projectiles moving slowly.

• Javelin: The shape and position of the javelin minimise drag. Athletes hold it with the point facing forward to cut through the air efficiently

• Long jump: while air resistance plays a smaller role, athletes often stretch out in flight to streamline their body shape, minimising drag and maximising distance.

Initial Speed (velocity) at release

• Javelin: athletes sprint down the runway to build momentum, increasing the speed of the throw. Strong upper body strength and well-timed release also contribute to maximum speed. d

• Long jump: jumpers accelerate as fast as possible before takeoff to transfer that horizontal speed into a powerful jump

Discuss how the factors that affect projectile motion can influence shot put technique(4)

• Bodies launched into the air (shot put) are subject only to the forces fo gravity and air resistance and are termed projectiles

• Speed of release is defined as the magnitude of the projectile’s velocity at the instant of release. The speed of release will determine the range

• The height of release, the greater the relative projection height, the longer the flight time and the greater the range

• The angle of release is defined as the angle between the projectile’s velocity vector and the horizontal at the instant of release

• Activities requiring maximum horizontal range, such as shot put, tend to use smaller angles than those in which maximum height is the objective

Explain how Newton’s laws of motion apply to shot put technique (3)

The shot put will remain stationary until the athlete forces it to initiate motion. Then the forces exerted by the athlete’s muscles will determine the acceleration of the shot. As the athlete pushes against the ground (action), the ground exerts an equal and opposite force (reaction), which helps generate the power needed for the throw.