Dropping Textbooks

Today, when I dropped my textbook in the back of the car, it made a loud thumping noise. Later, I dropped my book on my bed, and it barely made any noise at all. Why was this, I wondered?

Physics, of course.


My bed is much more soft and squishy than the floor of the car, so when the textbook falls onto it the book sinks in. This makes the time of the collision much longer than when it falls on the hard floor. Since J (impulse) = change in time x force. If you say that each time the book was dropped from about the same height, the initial velocity before the book impacted was about the same. The final velocity will always be zero, after it hits the surface. This means that the impulse was the same in both collisions, the collision with my bed and with the car floor. J/t = F, so the greater the time, the less the force. The time in the collision with my bed is much longer than the collision with the car floor, so the force in the first collision is less. The greater the force, the more noise the collision makes.