GCSE Physics - Momentum Part 2 of 2 - Changes in Momentum #60

Summary

This video explains how forces can change an object's momentum by accelerating or decelerating it. The concept of momentum, defined as mass times velocity, is demonstrated with examples. The video walks through calculations of force using changes in momentum over time, with an example involving a ball's acceleration. It also highlights how car safety features like crumple zones, seat belts, and airbags reduce injuries by spreading out the momentum change, thereby decreasing the force experienced during collisions.

Takeaways

• ⚖️ Momentum is calculated by multiplying mass by velocity.
• 🔄 Applying a force in the same direction of motion will increase the object's momentum.
• 🔢 To find the force required to change momentum, divide the change in momentum by the time over which the change occurs.
• 📏 The change in momentum equals the final momentum minus the initial momentum.
• ⏱️ Example: A force of 12 newtons was required to increase an object's velocity over 0.5 seconds.
• ⚙️ Formula for force can be written as (mv - mu) / t, where 'v' is the final velocity and 'u' is the initial velocity.
• 🏐 Example problem: Accelerating a 600-gram ball to 14 m/s in 0.1 seconds requires 84 newtons of force.
• 🚗 During car crashes, momentum reduces almost instantly, causing large forces and potential injuries.
• 💡 Safety features like crumple zones, seat belts, and airbags extend the time to reduce momentum, thereby lowering impact force.
• 🛡️ Increasing the time over which momentum changes reduces the force on passengers, decreasing injury risk.

Q & A

What is the relationship between force and momentum change?

Force is equal to the change in momentum divided by the time over which the change occurs. This means that the larger the change in momentum or the shorter the time, the greater the force applied.

How do you calculate momentum?

Momentum is calculated by multiplying an object's mass by its velocity. For example, if a 2 kg object moves at 5 m/s, its momentum would be 2 × 5 = 10 kg·m/s.

How does applying a force affect an object's momentum?

Applying a force in the direction of an object's motion causes it to accelerate, which increases its velocity and, in turn, increases its momentum.

What equation is used to calculate the force required to change momentum?

The equation to calculate force is: force = (final momentum - initial momentum) / time, or in another form, force = (mv - mu) / t, where 'v' and 'u' are final and initial velocities, respectively.

How do crumple zones in cars help reduce the risk of injury?

Crumple zones increase the time it takes for the car to lose momentum during a crash, reducing the force experienced by the occupants, which helps lower the risk of injury.

What is the purpose of seat belts in reducing injury during a car crash?

Seat belts prevent occupants from being thrown out of the car, and their slight stretchiness allows for a slower deceleration, reducing the force exerted on the body during a crash.

How do airbags contribute to safety in a collision?

Airbags compress during impact, increasing the time over which the momentum is lost, thereby reducing the force exerted on the person and lowering the risk of injury.

How can you calculate the force required to accelerate a 600-gram ball from rest to 14 m/s in 0.1 seconds?

The force is calculated by first determining the change in momentum, then dividing it by the time. The change in momentum is (0.6 × 14) - (0.6 × 0) = 8.4 kg·m/s. Dividing by 0.1 seconds gives a force of 84 N.

Why does a rapid decrease in momentum during a car crash cause injuries?

A rapid decrease in momentum results in a large force acting on the occupants of the car, which can cause injuries like head trauma or spinal damage.

What general principle do safety features like helmets and crash mats use to reduce injury?

Safety features like helmets and crash mats increase the time over which the momentum is lost, reducing the force on the person and minimizing injury risk.