The first law states that a body at rest will stay at rest until a net external force acts upon it and that a body in motion will remain in motion at a constant velocity until acted on by a net external force. Net external force is the sum of all of the forcing acting on an object.

Gravitational pull on the mass of the body i.e. the weight of the body acting downwards perpendicular to the horizontal plane at which the body is resting. Normal reactive force exerted on the body by the horizontal plane which is exactly opposite to the direction of the above mentioned force.

When more than one force acts on an object it is the net force that is important. Since force is a vector quantity, use geometry instead of arithmetic when combining forces. External force: For a force to accelerate an object it must come from outside it. You can’t pull yourself up by your own bootstraps.

When vectore sum of all external forces is zero a body at rest will continue to be at rest .

Yes. A body can remain in rest even when external forces are acting on it. Reason: According to Newtons First Law of Motion, an object at rest or uniform motion continues to remain in the same state unless and until acted upon by an unbalanced external force.

Answer. Answer: Balanced forces do not cause any change of state of an object. False.

Answer. Answer: There is no unbalanced force acting upon the book and thus the book maintains its state of motion. When all the forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerate.

The object will speed up, slow down or change direction. An unbalanced force (net force) acting on an object changes its speed and/or direction of motion. If however, the forces are balanced (in equilibrium) and there is no net force, the object will not accelerate and the velocity will remain constant.

Braking forces

1. However, the braking distance increases four times each time the starting speed doubles. This is because the work done in bringing a car to rest means removing all of its kinetic energy.
2. Work done = kinetic energy.
3. Work done = braking force × distance.