Force

Force and Energy Push And Pull Are Force 1. A force acts upon an object when the object is pushed or pulled. 2. The following diagrams shows activities that involve pushing forces.

Activities that involve pushing forces 3. The following diagrams show activities that involve pulling forces.

Activities that involve pulling forces

4. Forces cannot be seen. 5.

Only the effects of a force can be felt and observed.

6. Force acting on an object can cause changes in the shape or movement of the object. 7.

Examples of pushing and pulling forces are shown below:

Activities that involve pushing and pulling

Effects of A Force 1. A force can cause a change in the motion and shape of an object. 2. When a force is applied to an object, the force causes changes. 3. Forces can cause: (a) A stationary object to move. (b) A change in the shape of an object. (c) A change in the initial location of an object. (d) A change in the direction of an object's movement. (e) A moving objects to move faster or slower (f) A moving object to stop. 4. A stationary object moves when it is pushed or pulled. 5. The ball shown in the figure below will start to move in the same direction as the force that is applied to it.

A ball, moves when force is applied 6. Pressing, bending and stretching can change the shape of an object.

(a) Bending

(b) Stretching

(c) Pressing

Force can change the shape of an object. 7. A force can change the direction of an object's movement.

(a)

(b)

Force can change the direction of an object's movement

Friction 1. Friction is a force that opposes the movement of an object. 2. Friction occurs when two surfaces are in contact with each other.

The direction of the friction is opposite to the direction of motion of the object 3. Friction is a type of force. 4. Friction slows down the movement of an object.

A ball moves faster on a glass surfaces.

A ball moves slower on sand paper.

5. Advantages of friction: (a) Allows us to walk or run without slipping (b) Allows a moving vehicles to slow down or stop (c) Friction between the surface of our palm and an object enables us to hold the object without dropping. (d) Friction produces heat that lights up a match. (e) Enables us to sharpen a knife. 6. Disadvantages of friction: (a) Produces heat that may spoil the object or machine. (b) Causes the soles of shoes and tires to wear out. (c) Produces squeaky noises that irritate the ear. (d) Friction opposes movement, hence making movement slower or more difficult.

EXPERIMENT Aim To study the effect of different surfaces on the movement of an object. Materials and apparatus Ping pong ball , wooden plank, rough sand paper, fine sand paper, glass pane, stopwatch

The thing that 1. Is kept the same: the height of the inclined plank, the ball 2. Is changed; the type of surface of the inclined plank. 3. Is measured: the time taken by the golf ball to reach the end of the plank. Steps 1. The first plank labeled M is left as it is. 2. The second plank labeled N is wrapped with the coarse sandpaper. 3. The third plank labeled O is wrapped with the fine sandpaper. 4. A glass pane is placed above the fourth plank labeled P. 5. The golf ball is held at the edge of the higher end of plank M. The stopwatch is started as soon as the ball is released. 6. The time taken for the ball to reach the end of the plank is recorded. 7. Steps (5) and (6) are repeated for the remaining planks. 8. The findings are recorded in the table below.

Observation

Discussion 1. What can you say about the time taken when the ping pong ball moves on (a) plank P? It takes the shortest time to reach the end of the plank (b) plank N? It takes the longest time to reach the end of the plank 2. Give an inference for each of the answer in Question 1. The ping pong ball takes the shortest time on surfaces P because surfaces P is the smoothest and produces the least friction. Plank N has the roughest surface, so the ping pong ball takes the longest time to reach the end of the plank.

Conclusion The smoother the surface, the weaker the force of friction that is produced.

Ways To Reduce Friction 1. Ways to reduce friction: (a) using rollers or ball bearing (b) using rollers or marbles (c) using talcum powder, oil, wax, grease, air cushions. (d) Using an aerodynamic shape. (f) Smoothening the surfaces. 2. Ways to increase friction: (a) using rough materials (b) making patterns on surfaces.