an object will not change its motion unless acted on by an unbalanced force
objects with larger mass require more force to accelarate
if object A externs a force on object B, the object B has to exert an equal force of magnitude and opposite direction on object A
a ball will continue rolling down a hill unless another force acts on it.
its easier to push an empty cart than a full one.
while walking, we push our feet backwards, the ground also exerts a forward force on our feet of equal magnitude in the opposite direction, which makes us move forward