joelee9300
Posts: 3
Joined: Tue Oct 17, 2017 5:39 am
Occupation: Parent

### Momentum

My son(8th grader) is doing an experiment on momentum. He is releasing a cart from the top of a ramp and setting the ramp at different angles and at the bottom of the ramp is a sled that the cart collides with and then he measures the distance the cart moved the sled. He is a little confused on how to explain in his research WHY speed increases with angle. His teacher taught the basics of momentum (for example the formula, how increasing mass and speed increases momentum). So how would you explain why speed increases with angle.

He needs to define momentum and also explain how speed affects momentum.

I appreciate your help.

Lisa

AeroSE
Expert
Posts: 15
Joined: Wed Aug 23, 2017 4:20 pm
Occupation: Aerospace Engineer

### Re: Momentum

Hi Lisa,

This sounds like a great experiment on momentum! This is a great way to visualize the relationship between momentum and velocity.

To describe why a steeper ramp will lead to the cart achieving a higher velocity, we will need to look at what forces are acting on the cart, leading to movement down the ramp. Since the cart is placed at the top of the ramp and released from a set position, the only forces acting on the cart, are gravity and the resultant force from the ramp. Due to Newtons third law, the ramp will only apply a force that is equal to the amount of force that is applied to it. This is represented by the fact that the cart is completely supported by the ramp and does not move the ramp during the run.

The force applied by gravity will be in the vertical direction only. So If the cart is place on a flat ramp, the cart does not move. But, if the cart is placed on a sloped ramp, then some component of gravity will not be opposed by the ramp. The component that is not opposed will result in the acceleration of the cart in the same direction. The greater the slope of the ramp, the closer the carts movement aligns with gravity and results in a larger component of the force being applied to accelerating the cart.

Hope this helps,

Mike

joelee9300
Posts: 3
Joined: Tue Oct 17, 2017 5:39 am
Occupation: Parent

### Re: Momentum

Thank you for that clear explanation, that was extremely helpful and fast.
I wanted to show you my son's conclusion also:

According to my data increasing the angle of the ramp increases the velocity of the cart and pushes the sled (at rest) forward
because the higher the velocity the more momentum. For instance, the averages of my groups trials are:
Ramp Angle at 15 degrees - Sled was pushed a distance of 34 cm
Ramp Angle at 20 degrees - Sled was pushed a distance of 36.3 cm
Ramp Angle at 25 degrees - Sled was pushed a distance of 41 cm
My hypothesis is, If you change the incline and increase the angle of the ramp the momentum will increase was correct because the higher the ramp the more velocity. This is supported because the faster object is going the harder it is to stop(P=MxV) and momentum is directly proportional to an objects mass and velocity which supports my hypothesis because my data shows how the higher the ramp is the more speed the cart gained and the more momentum was transferred to the sled (at rest) which moved the sled a further distance.

Limitations
The experiment could be better if we documented the mass of the cart and also the length of the incline. The sled moved forward so we can guess that the cart's mass was greater than the sled.

cumulonimbus
Former Expert
Posts: 102
Joined: Thu Aug 17, 2017 9:23 am
Occupation: Student

### Re: Momentum

Hi,

Looks like your son is on the right track! I would also suggest including AeroSE's explanation of why a higher angle increases the momentum due to the greater effect of gravitational force. Regarding the "limitations" section, do you still have the cart and the ramp you used? In that case, you could mass the cart and find the length of the incline at this point. Also, it is usually standard to include a section about errors in the procedure/measurement error as well as how these errors could be improved and/or future questions for further study. If your son has further questions, make sure to check the Science Buddies conclusion-writing guide: https://www.sciencebuddies.org/science- ... #checklist
I hope this was helpful!

Elena

Return to “Grades 6-8: Physical Science”