Applying Newton's Laws of Motion

Principle of Stability

A larger base of support, a lower center of mass, a larger mass and a line of gravity within the base of support provides greater stability.

Example: a basketball player widens their stance and lowers their body when preparing to jump or absorb contact, maintaining balance and generating more power.

Principle of summing joint forces

When the forced created by our muscles combine at our joints to allow us to execute powerful movements

Example: javelin throw - the thrower starts by driving force from the legs, then rotates the torso, followed by the shoulder, elbow, and finally the wrist.

This sequence from large to small muscle groups builds up maximum force to launch the javelin further

Principle of impulse direction

The direction in which force is applied determines the direction of motion

Example: a footballer applies force on the side of the ball to make it move sidewards

Principle of linear momentum and linear impulse

Momentum = mass x velocity

Impulse = force x time

A greater impulse results in greater momentum

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

Principle of Angular Motion

Occurs when force is applied further away from the center of mass (eccentric force) causing an object or body to rotate

This creates torque - a turning force that results in rotation

The speed and control of this rotation are influenced by the objects moment of inertia (how mass is distributed around the axis)

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

Principle of Angular Motion

Center of mass

Average position of all the mass in an object or person

Changes based on body position because when you move your limbs or change your posture, the distribution of your body weight

Example: when you bend your knees, your center of mass lowers

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

• Conserved in a closed system (no external forces acting on it)

Application: athletes adjust body positions to control moment of inertia. Tucking the body during rotation reduces the moment of inertia, increasing spin speed, while extending the body before landing increases moment of inertia, slowing the rotation for control.

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

Application: when an athlete pushes off a platform, they generate angular momentum. As they rotate, their angular momentum remains constant, allowing them to perform spins or flips. By adjusting their body position, they can control spin speed (angular velocity) while conserving angular momentum.

Angular velocity: rate of rotation around an axis (measures in degrees per second or radians per second)

Application: When an athlete increases the speed of their movements, they increase the angular velocity resulting in faster rotation or movement. In certain sports, building up angular velocity before releasing an object increases its speed and distance.

Moment of inertia increases = angular velocity decreases