1. Hey Guest! Check out the 3 MCAT Study Plan Options listed in the 'stickies' area at the top of the forums (BoomBoom, SN2ed, and MCATJelly). Let us know which you like best.

    Also, we now offer a MCAT Test-Prep Exhibitions Forum where you can ask questions directly from the test-prep services.
    Dismiss Notice
  2. Dismiss Notice
  3. Download free Tapatalk for iPhone or Tapatalk for Android for your phone and follow the SDN forums with push notifications.
    Dismiss Notice
Dismiss Notice

Interview Feedback: Visit Interview Feedback to view and submit interview information.

Interviewing Masterclass: Free masterclass on interviewing from SDN and Medical College of Georgia

Dismiss Notice
Hey Texans—join us for a DFW meetup! Click here to learn more.

EK & Friction in the direction of motion

Discussion in 'MCAT Discussions' started by Actiq, Nov 17, 2005.

  1. Actiq

    Actiq New Member

    Joined:
    Oct 27, 2005
    Messages:
    3
    Likes Received:
    0
    Status:
    Pre-Medical
    Can anyone explain how friction can be in the direction of the net force as explained in EK physics Lecture 2.
     
  2. Note: SDN Members do not see this ad.

  3. Sicilian

    Sicilian Senior Member
    5+ Year Member

    Joined:
    Aug 8, 2005
    Messages:
    264
    Likes Received:
    0
  4. Nikki2002

    Moderator Emeritus 7+ Year Member

    Joined:
    Jun 16, 2005
    Messages:
    13,152
    Likes Received:
    2
    Status:
    Medical Student
    found the ek physics book to be confusing as hell....esp. that part about torque with the rhino...ugh i will see that in my nightmares. I liked the physics section from the kaplan comprehensive book much better.
     
  5. shantster

    shantster Eye protection!
    10+ Year Member

    Joined:
    Feb 10, 2005
    Messages:
    2,472
    Likes Received:
    0
    Status:
    Resident [Any Field]
    I haven't gotten to that point in the EK series, but I remember learning this in physics.

    Say you have a pick up truck and a box is in the tailgate. (Let's just pretend this is a Caddilac truck with it's carpeted tailgate so we have lots of friction :p ) You accelerate in the forward direction and the box does not slide. The net force is in the direction that the truck is moving because the acceleration is in that direction. The friction between the box and the tailgate is also in that direction because otherwise the box would slide towards the back of the tailgate. If you think about it, the box would want to stay in the same place that it was before the truck began moving and so if there was no friction between the two, it would slide off the back of the tailgate. Thus, the friction is occurring opposite to the direction of motion that the box wants to go (backwards) and so it is in the same direction as the net force (forward).

    Hope that helps!
     
  6. gujuDoc

    10+ Year Member

    Joined:
    Feb 21, 2004
    Messages:
    13,877
    Likes Received:
    34
    Status:
    Medical Student, Resident [Any Field]
    I used TPR for Physics because I didn't like the way EK explained everything. There were just a couple of pointers i took from the EK physics book, because TPR books didn't cover them.
     
  7. Actiq

    Actiq New Member

    Joined:
    Oct 27, 2005
    Messages:
    3
    Likes Received:
    0
    Status:
    Pre-Medical

    Hey!
    Thanks, that does help.
     
  8. osli

    osli Senior Member
    5+ Year Member

    Joined:
    Oct 13, 2005
    Messages:
    1,279
    Likes Received:
    6
    Status:
    Medical Student
    Just remember that a static friction force is always opposed to the direction that the "sliding" object would want to move, and that for dynamic friction it always opposes the direction of motion of the sliding object. i.e., it is essentially the same in both cases.

    You push on a box... it wants to move in the direction your hand pushes it... the friction force opposes and pushes back towards your hand. If you push hard enough to overcome the static friction force, the box moves, but still with a friction force pushing back towards your hand.

    The box in the pickup truck... inertia causes the box to want to move towards the rear relative to the truck... friction opposes and keeps it still. If you accelerate hard enough to overcome the static friction force, the box moves towards the rear, but still with a friction force opposing its motion.

    You have a box on a board, and start tilting the board... gravity pulls on the box and it wants to slide down the board... static friction opposes this tendancy and pushes back, keeping the board in place. If you tilt the board enough to overcome the static friction force, the box slides but with dynamic friction opposing its motion.

    i.e., static friction keeps things in place when they want to move by opposing the force trying to move them. Dynamic friction pushes back against the direction of motion and can be thought of as what keeps the box from sliding really fast down the board, or accelerating quickly when you push on it.
     
  9. Cooolguy

    Cooolguy Senior Member
    7+ Year Member

    Joined:
    Jul 17, 2005
    Messages:
    232
    Likes Received:
    0
    ek physics sucks. period.
     
  10. abyssinianson

    abyssinianson Junior Member
    5+ Year Member

    Joined:
    May 18, 2005
    Messages:
    51
    Likes Received:
    0

Share This Page