Riley is doing an experiment working with friction. he wants to find two ways to modify an object that could increase or decrease the same type of friction

As we know that friction force is a contact force which opposes the relative motion between two surfaces in contact.

So here we can change the force between two surface when they move relative to each other.

Here when Lubrication is used between two surface then the relative motion of two planes becomes easy. So by lubrication of the surface either by oil or by smoothing the plane we can say that friction force will be reduced.

Also friction force depends on the effective contact points between two surfaces. So as we increase the contact points between two surfaces then the effective frictional force will increase.

Also we know that friction force is given by

now as we increase the normal force between two contact planes either by increasing the weight or by applying normal external force we can say that friction force will increase.

connect the batteries in series and hope

80cm/s.

24cm/s.

53.3cm/s.