Unbalanced forces

Unbalanced forces

Unlike balanced forces, we say unbalanced forces when two forces acting on an object are not equal in size.

Unbalanced forces causes can cause:

a still object to move

a moving object to speed up or slow down

a moving object to stop

a moving object to change direction

Unbalanced forces make the wagon in the diagram speed up.

Notice that because there is a bigger force and a smaller force involved, the direction of the wagon will be determined by the bigger force. The wagon is moving as a result of unbalanced forces.

Resultant forces

To understand resultant forces better, let us see these two scenarios:

Any time a stationary object stays still, its resultant force is zero. As soon as force is applied, acceleration begins. The speed of the acceleration will depend on the force applied and the mass of the object.

Similarly, each time an object in motion (in a constant speed and same direction) stays in motion, its resultant force is zero too. As soon as a force is applied, it can make it stop, change direction, move slower or move faster. The effect will depend on the force applied and the mass of the object.

It is worth noting that an object may have several different forces acting on it. See the example in the illustration

Frictional forces

Friction is a force that stops things from moving easily.

Whenever an object moves or rubs against another object, it feels frictional forces. These forces act in the opposite direction to the movement. Friction makes it harder for things to move.

In the illustration below, the smooth base of the snowblades slides smoothly on the snow. The boy on the grass is having difficulty sliding because the grass is not smooth and his shoes are getting stuck in the grass. There is more friction between the shoes and the grass than the snow and the snowblades.

Without frictional forces, a moving object may continue moving for a longer period. Frictional forces are usually greater on rough surfaces than on smooth surfaces.

Frictional forces can be good and helpful. For example:

A basketball star can grip a ball and control it better in a dunk because of greater friction.

When we walk, we don’t slip easily because of the friction between our shoes and the floor.

Each time you ride your bike, friction between the tires and the road helps you not to skid off.

Sometimes frictional forces can be unhelpful.

If you don’t lubricate your bike regularly with oil, the friction in the chain and axles increases. Your bike will be noisy and difficult to pedal.

Air resistance

Let’s consider this quick experiment:Find three letter-size sheets of paper (or 3 A4-sheets).

Keep the first sheet (A) free from folding. Crush the second sheet (B) a bit, and crush the third sheet (C) into a small lump. Now, take the pieces of paper to the highest floor in your school and let the three paper specimens drop to the ground.

Which one fell to the ground first? Which one was last to reach the ground?

Between the ground and the highest point, there is air. The pieces of paper had to find their way down through the air. The smallest had very little work to do because it was small. The larger surface paper had more work to do because its large surface area meant that it had to work harder to overcome the air resistance. As the objects fell to the ground, the air was trying to prevent them from falling. That was air resistance.

Moving objects like aircraft, cars, and arrows experience air resistance when they are in motion. Frictional forces of the air against the moving object cause this resistance. There is more resistance with faster movement and less resistance with slower movement.

Note that the bigger the surface area an object has, the greater the air resistance. That is why airplanes and fast trains have pointed heads to help overcome air resistance. 

Have you seen bike riders in a race? They wear smooth clothing and helmets designed to overcome resistance. This makes them glide through the air at top speed.

that's all for now