Q5 of 18 Page 12

What is easier to move a box from rest, or to move it when it is already in motion? 

When the box starts sliding, the contact points on its surface, do not get enough time to look into the contact points on the floor. So, the sliding friction is slightly less than the static friction and you find it easier to move the box already in motion than to get it started.

More from this chapter

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3 What is the cause of friction? 4 Answer the following. (a) A ball is rolling on a road towards the north. What will be the direction of the frictional force acting on it?(b) If the direction of movement in the above case is changed to the south by applying force, then what will be the direction of the frictional force? 6 Does the smoothness of the sliding surface affect friction? Explain. 7 Why the friction between two surface increases when they are pressed harder. Give an activity to show the above effect.