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Sliding Friction: Follow Leftward Motion

In these separate paper-model trials, a crate already slides left across a stationary level floor. Only a leftward push and sliding friction act horizontally. No equipment or lifting is needed.

All worksheets

Watch the lesson | Compare the rightward-slide worksheet

5 questions0m 0s
Learn the skill

While the crate slides left, its stated sliding friction is 4 N right. Compare forces without confusing force direction with motion direction. Net force left speeds this leftward slide up; net force right slows it. Balanced forces keep its present velocity.

Worked example

In a different trial, push 12 N left and sliding friction 5 N right give net force 7 N left. The crate is already sliding left, so it speeds up left. An equal 5 N push instead would keep its velocity unchanged.

An already-leftward-sliding crate has twelve newtons pushing left and five newtons of friction right, giving seven newtons net left.
Worked example uses 5 N sliding friction. The questions use 4 N instead.
Question 1 Already sliding left: push 13 N left, sliding friction 4 N right. What is the net horizontal force?
Question 2 Already sliding left: push 4 N left balances sliding friction 4 N right. What happens to its velocity?
Question 3 The push is removed while the crate still slides left. Sliding friction remains 4 N right. What happens during that leftward slide?
Question 4 It has now stopped with no horizontal push or other horizontal force. What horizontal friction applies next?
Question 5 A person starts a step toward the left. Their planted foot pushes the ground right without slipping. Can static friction from the ground push that foot left?

Further inquiry

Invent three already-leftward-sliding trials with friction 7 N right. Choose pushes that speed up, maintain and slow the leftward motion. After a no-push trial stops, explain why you must change the friction rule.

Review criteria

  • State the initial leftward motion and the rightward sliding friction.
  • Choose leftward pushes above, equal to and below 7 N, and label each net force.
  • Separate slowing from immediate reversal; recheck contact state after stopping.