B.2.1 Newtons laws of motion IB SPORT

How can the motion of an object be described?

Using speed, velocity, and acceleration.

What determines the resultant motion of an object?

The sum of all forces acting on it (Newton’s Second Law).

What factors affect an athlete’s stability?

• Height of centre of mass relative to support base

• Size of support base

• Position of line of gravity relative to support base

• Mass of the athlete

What is the principle of summing joint forces?

Maximum force is generated by coordinating multiple body segments in sequence, usually from large to small segments.

How does linear motion relate to impulse?

Greater impulse applied → greater change in linear momentum.

What is the principle of impulse direction?

The direction of the impulse applied determines the direction of the resulting motion.

How is angular motion produced?

By applying a force at a distance from the centre of mass (eccentric force), producing rotation.

When is angular momentum conserved?

When an athlete or object is free of additional eccentric (external) forces, angular momentum remains constant.Define eccentric force.

Define eccentric force.

A force applied away from the centre of mass that produces angular motion.

What is impulse?

The product of force × time over which the force is applied; it changes the momentum of an object.

Why does increasing impact duration reduce force felt?

Longer impact time → same momentum change over more time → lower average force.

How does mass influence momentum in contact sports?

Greater mass → more momentum at the same velocity → harder to stop and more stable.

How do padded gloves reduce impact?

• increase impact duration → reduce peak force

• Spread force over a larger area → reduce pressure

• Absorb energy → reduce acceleration on the hand

What is the difference between speed and velocity?

• Speed = how fast an object moves (scalar, no direction)

• Velocity = speed with direction (vector)

How does Newton’s First Law relate to motion?

An object remains at rest or in uniform motion unless acted on by an external force.

How does Newton’s Second Law relate force, mass, and acceleration?

F=ma; the acceleration of an object is proportional to the net force and inversely proportional to mass.

How does Newton’s Third Law apply in sport?

Every action has an equal and opposite reaction.
Example: A sprinter pushes backward on the blocks → the blocks push the sprinter forward.

What is linear momentum?

The product of mass × velocity; it describes the motion of an object in a straight line.

How can athletes increase linear momentum?

Increase mass, velocity, or impulse applied during contact.How does the line of gravity affect stability?

How does the line of gravity affect stability?

If the line of gravity falls within the base of support, the athlete is stable; if it falls outside, the athlete may tip over.

How does base of support affect stability?

A larger base of support increases stability; a narrow base reduces stability.

How does height of the centre of mass affect stability?

A lower centre of mass → more stability; a higher centre of mass → less stability.

What is moment of inertia?

A measure of an object's resistance to angular acceleration; depends on mass distribution relative to axis of rotation.

How can an athlete increase angular velocity during a rotation?

Decrease moment of inertia (e.g., tuck in arms or legs) → spin faster while conserving angular momentum.

Give an example of angular motion in sport.

• Gymnast twisting in the air

• Diver spinning during a somersault

• Tennis player hitting a topspin shot

What is the principle of impulse direction in sport?

The direction of the applied impulse determines the direction of resulting motion (e.g., kicking the ball at an angle changes its trajectory).

Why does follow-through in striking sports (e.g., golf, tennis) help increase momentum transfer?

Follow-through extends contact time, increasing impulse → more momentum transferred to the ball or object.

How does reducing moment of inertia affect angular momentum if no external torque acts?

Angular velocity increases to conserve angular momentum (L=IωL=Iω).

How does a rugby player use mass and momentum to make a tackle more effective?

Greater mass → more momentum at the same speed, making it harder to stop the opponent and increasing stability during contact.

How do padded gloves in boxing or hockey reduce impact on the hand?

• Increase contact time → reduces peak force

• Spread force over a larger area → reduces pressure

• Absorb energy → reduces acceleration of the hand

How does a long jumper maximize takeoff velocity using impulse?

By applying a large force over a longer time on the takeoff board → increases linear momentum and horizontal velocity.

How does a diver increase angular velocity during a somersault?

By tucking tightly (reducing moment of inertia) → angular velocity increases to conserve angular momentum.

How does a gymnast initiate a twist in mid-air?

By applying an eccentric force off the centre of mass (e.g., pushing off with one hand) → produces angular motion.

Why is follow-through important in striking sports (tennis, golf, baseball)?

Extends impact time, increasing impulse → greater momentum transfer to the ball or object.

How does a basketball player increase jump height using Newton’s laws?

Applies a large force against the ground (Newton’s Third Law) → acceleration upward increases → higher jump.

How does base of support affect stability in wrestling or rugby?

A wider stance increases stability; a narrow stance reduces stability and makes the athlete easier to push or topple.

How does a soccer player curve a ball using eccentric force?

Strikes the ball off-centre, creating angular motion (spin) that curves the ball during flight.

How do athletes use the principle of impulse direction in throwing or hitting?

The direction of force applied determines the path of the object, e.g., throwing a javelin at an angle or kicking a ball diagonally.

How does a tennis player manipulate moment of inertia during a serve?

Tucking arms or rotating torso efficiently reduces moment of inertia in certain axes → increases angular velocity and spin.

How does line of gravity position affect a sprinter in a start or push-off?

Forward lean moves the line of gravity ahead of base of support → generates forward acceleration while maintaining balance.

How can a sprinter increase their linear momentum during the race?

By increasing mass (e.g., using heavier shoes or weights) or by increasing velocity (e.g., improving acceleration).

What is the equation for impulse?

Impulse=F×Δt

• F = force applied

• ΔtΔt = time over which the force is applied

Q: How does a boxer increase impulse during a punch?

By applying a large force over a longer time (e.g., through a punch follow-through) → increases impulse and momentum transferred to the opponent.

How does a gymnast conserve angular momentum during a somersault?

When the gymnast tucks in, the moment of inertia decreases → angular velocity increases to conserve total angular momentum.

How does the equation for force (F=maF=ma) apply to a rugby player tackling an opponent?

The player increases the force applied by either:

• Increasing mass (by running at a higher speed), or

• Increasing acceleration (by pushing harder into the tackle).
  This greater force leads to a higher change in momentum of the opponent.

A footballer kicks a ball with a velocity of 20 m/s. If the ball has a mass of 0.45 kg, what is its linear momentum?

Momentum= m×v = 0.45kg×20m/s = 9kgm/s

If a swimmer applies a force of 50 N over 0.3 seconds, what is the impulse?

Impulse=F×Δt=50N×0.3s=15N

How does moment of inertia affect a skater’s spin?

The skater reduces moment of inertia by pulling arms inward → angular velocity increases (conserving angular momentum).

A tennis player hits a ball with a force of 100 N for 0.2 seconds. How much impulse does the ball experience?

Impulse=F×Δt=100N×0.2s=20N

How does Newton's Second Law apply in sports?

It explains how force and acceleration are related:

• Increasing force increases acceleration.

• Decreasing mass increases acceleration.
  Example: In a sprint, a higher force from the legs (and less body mass) will accelerate the athlete faster.

A skater with a mass of 70 kg pushes off a wall. If the skater accelerates at 2 m/s², what is the force exerted?

F=m×a=70kg×2m/s2=140N

a ball drops from rest for 3 seconds, accelerating at 10 m/s squared. what is its final velocity?

30 m/s