Newtons Laws
In a football match, why does a stationary ball remain still until it's kicked?
Because of Newton’s First Law – an object remains at rest unless acted upon by an external force.
What is the definition of velocity in biomechanics?
Velocity is the rate of change of displacement over time, and it includes direction.
What is the difference between balanced and unbalanced forces?
Balanced forces are equal and opposite, causing no change in motion. Unbalanced forces cause acceleration or deceleration.
What 2 forces would be drawn from the CoM in a free body diagram?
Air resistance and Weight
What is limb kinematics?
The study of movement in relation to time and space.
A sprinter applies greater force to the blocks at the start of a race. What effect does this have on acceleration and why?
Acceleration increases because, according to Newton’s Second Law, force is directly proportional to acceleration (F = ma).
What is the equation used to calculate acceleration?
Acceleration = (Final velocity – Initial velocity) ÷ Time
What is meant by net force?
Net force is the overall force acting on an object after all forces have been added or subtracted. It determines whether the object will remain still/accelerate/decelerate.
What 2 forces should be drawn from the PoC in a free body diagram?
Friction and Reaction
How does 3D limb kinematics analysis work?
It uses infra-red cameras that track reflective markers placed on joints to measure angles, velocity, and acceleration of movement.
When a gymnast pushes down on the vaulting table, why do they lift off into the air?
Newton’s Third Law: for every action, there is an equal and opposite reaction. The push down on the vault creates an upward reaction force that propels the gymnast.
A rugby player increases their mass and maintains the same velocity. How does this affect their momentum?
Their momentum increases because momentum = mass × velocity. Increasing mass increases momentum if velocity stays the same.
Name the two vertical forces acting on a gymnast standing still on a beam and explain their interaction.
Weight (downward) and reaction force (upward). They are equal and opposite, so the gymnast remains in equilibrium.
What is the centre of mass?
The point at which the body’s mass is considered to be concentrated and balanced in all directions.
What do force plates measure, and give one example of a sport they benefit.
Force plates measure ground reaction forces. They benefit sports like long jump, sprinting, or weightlifting to analyse power output and technique.
During a rugby tackle, explain how all three of Newton's Laws can be seen in action.
1st Law: The runner continues forward until tackled (external force).
2nd Law: The harder the tackler hits (more force), the greater the deceleration.
3rd Law: The tackler exerts force on the runner; the runner exerts an equal and opposite force back.
A sprinter with a mass of 70 kg accelerates at 3 m/s². Using Newton’s Second Law, calculate the force they produce.
Force = mass × acceleration
= 70 × 3 = 210 N
Which two horizontal forces act on a 100m sprinter during a race, and how do they affect motion?
Friction (helps propulsion) and air resistance (opposes motion). If friction is greater than air resistance, the sprinter accelerates.
How does lowering the centre of mass affect a performer’s stability?
Lowering the centre of mass increases stability by making it harder for the line of gravity to fall outside the base of support.
How do wind tunnels help improve performance in sports like cycling?
Smoke is pushed through a fan at high speed (e.g. 600 rpm) to simulate air flow. Equipment inside measures the force of air resistance on the body or bike to improve aerodynamics.
What does inertia mean, and how is it demonstrated when a netball player suddenly changes direction to dodge a defender?
Inertia is an object’s resistance to a change in motion. In netball, the player’s body wants to keep moving in a straight line at the same speed. Changing direction requires force to overcome this inertia and alter their motion.
A sprinter runs the first 50m of a 100m race in 6.0 seconds, and the second 50m in 4.0 seconds. In which half was their average velocity greater, and why?
The second 50m — because velocity = distance ÷ time.
First 50m: 50 ÷ 6 = 8.33 m/s
Second 50m: 50 ÷ 4 = 12.5 m/s
A cyclist applies 600 N of force through the pedals. Air resistance and friction total 500 N in the opposite direction. What is the net force, and what does it mean for the cyclist?
Net force = 600 N – 500 N = 100 N forward. The cyclist will accelerate because the forces are unbalanced.
A long jumper is on the take off board. Draw and label a free body diagram with the correct forces acting and their directions.
Weight and Air Resistance must come from CoM in a right angle with AR opposing DoM and Weight going down. Friction and Reaction must come from the PoC of foot on take off board, in a right angle with F going in DoM and R going up. All must be drawn with arrows.
Give one advantage and one disadvantage of using limb kinematics in elite sport.
Advantage: Provides detailed feedback on technique to improve performance or reduce injury risk.
Disadvantage: Expensive and requires specialist equipment and expertise to interpret data.