From harms of friction forces .................................... .

Friction is a resistance force originated between ......................................... .

When an object transfers from the equator to the north pole, ..................... is changed.

The violin and the guitar are among ....................... musical instruments.

Flute and reed pipe are among ..................... musical instruments.

When an object transfers from the equator to the north pole, ..................... remains fixed.

The effect that attempts to change the object's state from being static to motion or vice versa.

Waves produced due to the vibration of medium particles.

........................ is motion of sound waves.

........................ is movement of the Moon around the Earth.

........................ is motion of the simple pendulum.

Ultraviolet rays are used in examining mineral raws in industry.

Dynamo changes the heat energy into electric energy.

Passengers are rushed forward when moving car stops suddenly.

Earth's gravitational force acceleration increases by approaching to the Earth's centre.

If you know that the Earth's gravitational acceleration is 9.8 m/ $s^2$  , so the weight of an object its mass is 70kg on Earth equals ......... newton.

....................... is the scientist who discovered the Earth's gravitational force.

The mass of a person at the equator is less that his mass at the two poles.

Brakes are from examples of forces inside living systems.

Object's weight = its mass + gravitational acceleration