Loading in 5 sec....

Dynamics: Cause of MotionPowerPoint Presentation

Dynamics: Cause of Motion

- 46 Views
- Uploaded on
- Presentation posted in: General

Dynamics: Cause of Motion

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Dynamics: Cause of Motion

Sections 7.1 , 7.2

- Test #2 has been moved from Tuesday next week to Thursday next week due to a need for more time to prepare for content.
- Addresses Chapters 4, 6, and 7.
- Next reading quiz due prior to class on Tuesday
- LAB A4-PM: Projectile Motion due Friday 4pm
- Weekly Reflection #7 sent out on Friday morning
- Final Exam Thursday, Dec 11, 10am-12:00pm

- Demonstration: the total momentum of an isolated system is conserved. That is, pi = pfif and only if we have an “isolated system” – no unbalanced outside forces.
- Example 1 – the collision of carts
- Example 2 – the “explosion” of carts
- Example 3 – the addition of mass

- A truck with a mass of 3,000kg and a velocity of +20m/s collides head on with a car of 1,500kg mass and a velocity of -20m/s. If the vehicles stick together, what is the resulting motion of the pair?
- Solve using conservation of momentum; that is, pi = pf.

- Two dynamics carts are separated by a compressed spring. The mass of cart 1 is twice the mass of cart 2; that is, m1=2m2. The spring is released and the carts fly apart. If cart 1 has a velocity of +3m/s, what is the velocity of cart 2?

- A train car (mass 11,200kg) is moving along at a speed of +2m/s. A 5,000kg mass of coal with no horizontal motion is dropped into the hopper of the train car. What is the resulting motion of the train car now loaded with coal?

- a.k.a. Newton’s Second Law
- The net instantaneous force acting on an object is precisely the instantaneous change of its momentum per unit time. In symbols, the second law can be written as F = Δp/Δt with Δt very small.
- Note that F and Δp are vectors.
- Not very enlightening; time for an experiment.

- Experiment:
- Acceleration as a function of force (constant mass system)
- Acceleration as a function of mass (constant force system)

- Results:
- a is proportional to F
- a is inversely proportional to m

- Conclusion: F = kma; k=1 if F defined to be in Newtons, N

- F = Δp/Δt
- F = Δmv/Δt
- F = mΔv/Δt
- F = ma
- Both F and a are vectors; m is a scalar.
- The sum of forces acting on a body produce an acceleration inversely proportional to mass.
- ΣF=ma (where F is expressed in Newtons)

- What is the weight of a person with a mass of 81kg. Note that g = 9.8m/s2.
- An car with a mass of 1,500kg accelerates at a rate of -2m/s2 under a constant force. What are the magnitude and direction of that force?
- How much force would it take to slow a 75kg person riding in a car going +20m/s to a complete stop if the time was 0.03 seconds – the typical time of an auto collision?

- An object accelerates at a rate of 1.5m/s2 under a force of 53N. What is its mass?
- How much upward force does the ground apply to someone with a mass of 75kg to counter balance the pull of gravity? Note that g = -9.8m/s2 and that Fnet = ma and that a = g.
- A force of 7.0N is applied to a 3.5-kg mass for 2.0 seconds. What is the change of velocity?