Newtons Third Law and The and Opposite Force Discussion


Now let’s consider forces and Newton’s Laws.  Discuss the following.  A box with a mass of 100 kg is on a frozen lake (no friction).  A force of 200 N to the left, and another force of 200 N to the right act on the box.  Describe the motion of the box.

Also, if a car with a constant speed is turning a level corner, is there a net force acting on the car?


Newton’s first law states that “ an object in motion stays in motions and an object at rest stays at rest, unless acted upon by an outside force”. If a box is acted upon by two equal forces, but in opposing directions, then the box will not move. The net force will be equal to zero.

If a car is going at a constant speed in a straight line, it will continue on forever until acted on by an outside force. When the car is turning the corner, the velocity changes leading to the acceleration to change as well. This force is called centripetal force around the curve.


2nd student

Newton’s first law states, “Every object remains at rest or in its state of uniform straight-line motion unless acted upon by an unbalanced force.” We also know that acceleration is equal to the force divided by the mass. Due to the forces in both directions on the box being equal the net force would equal zero. Since the force equals zero then the acceleration would also be zero. The box is not moving while on the ice since it is at rest and there is not an unbalanced force acting on the box. Newton’s third law states, “Whenever two objects interact, the force exerted on one object is equal in size and opposite in direction to the force exerted on the other object.” Therefore, the box is pushing down on the frozen lake with the same amount of force as the frozen lake is pushing up on the box due to the box not moving up or down.

In the scenario of the car turning a level corner, we know that a force must be acting on the car to turn due to what is described in Newton’s first law when he mentions that an object remains in its straight-line motion unless acted upon by an unbalanced force. As the car is turning there in a change in the car’s velocity due to its direction being changed. This is turn impacts the car’s acceleration and the force that is pulling the car out of its straight-line path is centripetal force.