⇒ We use the term linear momentum when we refer to collisions (or explosions) that take place in one dimension i.e. along a straight line

⇒ This shows a demonstration of a small one-dimensional explosion

• The head of a match has been wrapped tightly in aluminium foil
• A second match is used to heat the foil and the head of the first match, which ignites and explodes inside the foil
• The gasses produced cause the foil to fly rapidly and the matchstick to fly in the opposite direction

⇒ In all collisions and explosions, both total energy and momentum are conserved, but kinetic energy is not always conserved

⇒ In this case, the chemical potential energy in the match head is transferred to the kinetic energy of the foil and matchstick, and also into thermal, light and sound energy

⇒ As the match head explodes, Newton's third law of motion tells us that both the matchstick and foil experience equal and opposite forces

• Since the forces act for the same time interval, both the matchstick and foil experience equal and opposite impulses, F▵t

⇒ Since F▵t = ▵(mv), it follws that the foil exactly the same positive momentum as the matchstick gains negative momentum

⇒ We can now do a vector sum to find the total momentum after the explosion:

⇒ So there is conservation of momentum: tht total momentum of the foil and matchstick was zero before the explosion, and the combined momentum of the foil and matchstick is zero after the explosion

⇒ Collision experiments can be carried out using gliderson linear air tracks

⇒ These can demonstrate the conservation of linear momentum

⇒ The air blowing out of small holes in the track lifts the gliders so that frictionoal forces are very small

⇒ Also see our notes on:

• Introducing Momentum
• Momentum and Impulse
• Momentum and Energy
• Elastic and Inelastic Collisions