SCIENCE: February 2009

FIRDAUS RIPIN

1. If we rub our palms together, we will fell our palms become warmer because friction produces heat.

2. If we try to move a heavy object, we will find that it is difficult to do so. This is because friction opposes the motion.

3. If we rub an eraser against a surface, we will find that the eraser becomes smaller. This is because friction causes wear and tear.

4. Also, without friction, an object cannot be placed in a fixed position.

2.3 Friction

FIRDAUS RIPIN

What is friction?

1. Friction is a force that opposes motion.

2. Friction exists when two surfaces are in contact against each other.

3. The direction of the frictional force is always opposite to the direction of movement of an object.

4. For example, a ball rolling on floor will eventually stop.

5. This happens because there is friction between the surfaces of the ball and the floor.

6. The friction opposes the motion of the ball, causing it to slow down an stop.

Apakah geseran?

1. Geseran ialah daya yang menentang pergerakan.

2. Geseran wujud apabila dua permukaan bersentuhan antara satu sama lain.

3. Arah daya geseran sentiasa bertentangan dengan arah gerakan objek.

4. Contohnya, bola yang sedang bergolek di atas lantai akhirnya akan berhenti.

5. Ini berlaku kerana wujud geseran antara permukaan bola dan lantai.

6. Geseran menentang pergerakan bola, menyebabkan bola bergerak lebih perlahan dan akhirnya berhenti.

LATIHAN 2

FIRDAUS RIPIN

Underline the correct words.

1. If the spring is (pulled, pushed) it becomes extended.

2. Rubber bands become (shorter, longer) when pulled.

3. A can becomes (pieces, dented) when it is hammered.

4. Plasticine becomes (flat,thick) when it is pressed.

5. A glass (breaks, dented) into pieces when it is dropped onto the floor.

LATIHAN

FIRDAUS RIPIN

A. Write True or False

1. A force can change the speed of a moving object. _____________

2. A force applied in the same direction of a moving object will cause the object to stop. _________

3. A force can change the direction of a moving object. ___________

4. A force makes a stationary object move. ___________

5. A force equally applied to a moving object makes the object move faster.__________

A Force Can Change the Shape of an Object

FIRDAUS RIPIN

A Force Can Change the Motion of an Object

FIRDAUS RIPIN

A Force Can Move a Stationary Object

FIRDAUS RIPIN

2.2 Effects of a Force

FIRDAUS RIPIN

1. A force can
a) move a stantionary object
b) change the motion of an object
c) change the shape of an object
2. During a football game, we can clearly observe the effects of a force to the motion of an object.

A Force Can Move a Stationary Object

1. A stationary ball will move when it is kicked.
2. A force is applied to the ball when it is kicked. This force causes the ball to start moving.
3. The ball moves in the same direction as the applied force.
4. The ball will move faster or roll further it we kick harder.

A Force Can Changes the Motion of an Object
1. The direction of the force applied to an object will determine its motion.
2. A moving ball will move faster if a force is applied in the same direction of its motion.
3. On the other hand, a moving ball will move slower if a force is applied in the opposite direction of its motion.
4. Also, a moving ball will change its direction when a force is applied from another direction when a force is applied from another direction of its motion.
5. A force can cause a moving object to stop.
a) For example, when a goalkeeper catches a moving ball with his hands, the ball will stop.
b) The goalkeeper exerts an opposing force on the moving ball by catching it.

A Force Can Change the Shape of an Object
1. A force can cause the shape of an object to change.
2. The changes of the objects when a force is applied may be temporary or permanent depending on the physical characteristic of the object.
3. Elastic objects such as the spring and rubber band only change shape when force is applied to them.
4. When the force is removed, the object returns to its original shape.
5. When force is exerted on a fragile object, the object will be broken apart. The change of shape is permanent.