Same change in momentum, different force.

• Linear momentum is p = mv, a vector along the velocity. Its SI unit is kg m s⁻¹.
• The second law: the net external force on a body equals the time rate of change of its momentum, F = dp/dt, and the momentum changes in the direction of that force. For constant mass this gives F = ma.
• The SI unit of force is the newton: 1 N = 1 kg m s⁻².
• The law is a vector equation and can be applied component by component; a force perpendicular to the velocity changes the direction of motion but not the speed.
• Acceleration at an instant depends on the force at that instant, not on the history of motion. A stone dropped from a moving train has, just after release, only the gravitational acceleration.
• Impulse is force multiplied by time for a force acting briefly, and it equals the change in momentum: J = FΔt = Δp. Its unit is N s, the same as momentum.
• The same change in momentum over a longer time needs a smaller average force; this is why a fielder draws the hands back while catching a fast ball.
• For a ball that rebounds, the change in velocity is the sum of the two speeds, because the direction reverses.

Teaching this idea? Put the simulation on your own page or LMS with this code.