B.2.1.1 (4) Applying Newton's law of motion

There are several principles to consider when applying Newton’s laws:

1. Principle of stability

The following factors affect the stability of an object:

• Height of the centre of mass relative to the supporting surface

• The size of the base of support (larger base = greater stability)

• The position of the line of gravity relative to the base of support (a line of gravity that is within the base of support provides greater stability)

• The mass (more mass = more stability

2. Principle of summing forces

• When you play sports, your muscles create forces to make movements which act on your joints, allowing you to perform a wide range of movements

• Each joint in your body can experience multiple forces acting on it simultaneously

3. Principle of impulse direction

• This principle in sport is to understand how to kick so it goes exactly where you want it to go. Impulse is a “pushing force” that you apply to the ball

• In sports involving a ball, understanding impulse direction helps athletes control the ball and make it go where they want.

• It’s all about applying the right amount of force in the right direction to make the ball go where you want it to go

4. Principle of linear momentum and linear impulse

• Momentum = mass x velocity

• Impulse = force x time

• A greater impulse (force applied over time) results in greater momentum

• A long follow-through in kicking a football increases impulse, generating more power and distance

5. Principle of angular motion

• Occurs when a force is applied away from the centre of mass, known as an eccentric force, causing an object or body to rotate. This creates torque

  • Torque - a turning force that results in a rotation

• The speed and control of this rotation are influenced by the object’s moment of inertia

• The product of the moment of inertia and rotational speed is called angular momentum, which remains conserved unless acted on by an external torque

  • Angular momentum: the quantity of rotation of a body, calculated as the product of inertia and angular velocity

  • Moment of inertia: refers to the resistance to rotational change, depending on how mass is distributed relative to the axis of rotation

  • Angular velocity: the rate of rotation around an axis

  • Conservation of angular momentum: states that in the absence of external forces, the angular momentum of a system remains constant. Athletes use this to control spin.