Impulse and change of momentum

Posted by Mr Mallon on October 30, 2013

When a car is in collision with a wall which brings it to a stop its momentum must be reduced to zero.

The change of momentum of the car is equal to the impulse it receives.

Impulse = change of momentum.
Ft = change of momentum

Now this change of momentum can come about with a LARGE FORCE acting over a small time or a small force acting over a LONG TIME.

The above movie shows the force time graph of two collisions of a car with a wall and then a collapsible wall.

Assuming the car is travelling at the same speed before each collision the change of momentum will be the same in each case.
You can calculate the change of momentum from the area of the force time graph. Note each graph has the same area but the time to change the momentum is different.

You will notice that in the collision with the collapsible barrier the time for the change in momentum is longer. This means that to keep the same area the peak force will be lower.

So to survive collisions it is important to increase the time you take to come to a stop. That is why car safety needs airbags, seat belts and crushable car fronts.

30Oct
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Virtual Momentum Investigation.

Posted by Mr Mallon on October 7, 2013

Use the above momentum simulation to investigate the total momentum before and after the trolleys collide.

  1. Click on the different stacked trolleys to change the mass of each vehicle`s mass.
  2. Press the green triangle to play the simulation
  3. Download the investigation sheet here Momentum investigation sheets.

Think of an object`s momentum as how hard or easy it is to stop the object from moving. Obviously it is much harder to stop a slowly rolling car than it is to stop a fast moving football.

Momentum depends on the object`s mass and velocity.

daum_equation_1381173460689

daum_equation_1381173354922

Momentum is a vector quantity which has units daum_equation_1381173682367

7Oct
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Higher Starter Question 003: Pushing Blocks!

Posted by Mr Mallon on February 2, 2013

Hi Physics lovers! Here is your starter question on pushing blocks.
Click the pause button in the movie to start it again.

2Feb
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Higher Starter Question 2

Posted by Mr Mallon on January 31, 2013

Hi physics lovers! Here is today`s starter question on finding the speed of a ball from the horizontal and vertical components of velocity.

31Jan
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