Momentum is a vector quantity that describes the “quantity of motion” of an object. It depends on mass and velocity, and its direction matches the object’s velocity. Objects with larger mass or higher velocity have greater momentum, making them harder to stop.
See how mass and velocity affect momentum, and how total momentum is conserved in collisions and explosions.
A lorry has much greater momentum than a car at similar speed because of its larger mass.
Total momentum before = total momentum after (no external force).
Momentum is a vector quantity that describes the “quantity of motion” of an object. Its direction matches the object’s velocity.
Momentum is calculated using \(p = mv\), where \(m\) is mass (kg) and \(v\) is velocity (m s\(^{-1}\)). The SI unit is \(\text{kg m s}^{-1}\).
Total momentum before a collision or explosion equals total momentum after, provided no external force acts: \(m_1u_1 + m_2u_2 = m_1v_1 + m_2v_2\).
Firemen hold hoses tightly to balance the water’s forward momentum (reaction force). In rocket launches, hot gases expelled downward propel the rocket upward, conserving total momentum.
Momentum
where \(p\) = momentum (kg m s\(^{-1}\)), \(m\) = mass (kg), \(v\) = velocity (m s\(^{-1}\)). Direction of momentum = direction of velocity.
Principle of Conservation of Momentum
Valid when no external force acts on the system. Applies to both collisions and explosions.
Answer in your mind, then press “Check Answer”.
A 600 kg bicycle moves at 10 m s\(^{-1}\). What is its momentum?
A 4 kg ball (5 m s\(^{-1}\)) collides with a 2 kg ball (0 m s\(^{-1}\)). After collision, they move together at 3 m s\(^{-1}\). Is momentum conserved?
Why do firemen need multiple people to hold a hose when water gushes out?
Momentum is a scalar quantity.
Momentum is a vector quantity — it has both magnitude and direction, matching the object’s velocity.
Only heavy objects have momentum.
Any moving object has momentum. A tennis ball moving fast has momentum, even though its mass is small.
Conservation of momentum applies only to collisions.
Conservation of momentum applies to both collisions and explosions (e.g., rocket launches), as long as no external force acts.
Objective: Identify momentum, conservation of momentum, vector quantity and SI unit.
1 What is the SI unit of momentum?
2 Which statement is true about conservation of momentum?
3 Momentum is a quantity.
4 The formula for momentum is \(p =\) .
Drag each term to the correct description. If using a phone, tap the answer first, then tap the matching box.
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