Momentum and Impulse

Question 1

Momentum, what is it and the equation for it:

Answer 1

• The quantity of (linear) motion that a body possesses
▫ Momentum (kg∙m/s) = mass (kg) × velocity (m/s)
 p = mv

• The momentum of a static object = 0 kgm/s, because velocity = 0 m/s
▫ To increase momentum we need a larger mass or higher velocity

• Generally of most importance in sports where collisions are involved
▫ “Size and speed”

Question 2

what is the conservation of momentum?

Answer 2

• Conservation of momentum
▫ In the absence of external forces, the total momentum of a given “system” remains
constant

• This extension is also applicable when two bodies collide and entangle together (e.g. rugby
tackle)

Question 3

what is impulse and what is the equation?

Answer 3

• The product of the force applied and the time over which that force was applied

• Impulse (N∙s) = force (N) × time (s)
• J = F × t

Question 4

what can impulse also be?

Answer 4

Impulse = mass × change in velocity

Question 5

impulse from Force-Time curves?

Answer 5

• We typically have phases of positive and negative impulses in human movement

▫ Positive – negative impulse
= total impulse

▫ Total impulse = overall Δ momentum (also Δ velocity)

Question 6

Antero-Posterior forces in running:

Answer 6

• In every step in walking/running/sprinting, we always experience a negative (braking) force followed by a positive (propulsive force)
• Because this graph is force (y-axis) against time (x-axis), the area under the graph = impulse (force × time)

This means that we have a phase of
negative impulse (negative force × time)
then a phase of positive impulse (positive force × time)

• The net impulse (i.e. positive minus negative) will give us the total impulse and tell us how
much the runner’s velocity changed during this ground contact phase (impulse = change in momentum)