• The force that makes things fall to the ground on Earth is called gravity.
• Gravity also holds Earth and the other planets in their orbits around the Sun.
• The force of gravity also exists on the moon but it is not as strong as it is on the Earth (this is because the moon is much smaller than the Earth).

Mass and Weight

• The mass of an object is how much matter it contains. It is measured in grams (g) or kilograms (kg) but is NOT a force.
• The weight of an object is the force caused by gravity pulling down on the mass of an object. It is measured in Newtons (N).
• Weight is measured using a forcemeter. The bigger the weight attached to the forcemeter, the more the spring inside the forcemeter stretches.

Forces

• Forces are just pushes and pulls in a particular direction.
• Forces are shown by arrows in diagrams. The direction of the arrow shows the direction in which the force is acting. The bigger the arrow, the bigger the force.
• If two forces are balanced, it means the forces are the same size but are acting in opposite directions.
• If two balanced forces are acting on an object, that object will not change its motion. If it is still, it will stay still. If it is moving, it will continue moving, in the same direction and at the same speed.
• Unbalanced forces can make objects start to move, speed up, slow down, or change direction.

This car will stay still because the forces acting on it are equal.	This car will move because the pushing force does not have a stronger or equal force pushing back on it.

Friction

• Friction is a force between two surfaces that are sliding, or trying to slide across one another, for example when you try to push a toy car along the floor.
• Friction always works in the direction opposite from the direction the object is moving, or trying to move. It always slows a moving object down.
• The amount of friction depends on the materials from which the two surfaces are made. The rougher the surface, the more friction is produced. For example, you would have to push a book harder to get it moving on a carpet than you would on a wooden floor. This is because there is more friction between the carpet and the book than there is between the wood and the book.
• Friction also produces heat. For example, if you rub your hands together quickly, they get warmer.
• Friction can be a useful force because it prevents our shoes slipping on the pavement when we walk and stops car tires skidding on the road.
• Ice causes very little friction, which is why it is easy to slip over on an icy day. But this is a good thing for ice skating and sledging.
• Sometimes we want to reduce friction. For example, moving parts inside a car engine are lubricated with oil, to reduce friction between them. The oil holds the surfaces apart, and can flow between them. The reduced friction means there is less wear on the metal, and less heat produced.

Air Resistance

• Air resistance is a type of friction between air and another material. When an airplane flies through the air, for example, air particles hit the airplane, making it more difficult for the airplane to move through the air.
• Some shapes, known as streamlined shapes, cause less air resistance than others. Airplanes and cars are streamlined, so that they move through the air as easily as possible.

If you have finished answering your questions, EXIT out of this page to the main WebQuest page.

Information from:
BBC Schools
http://www.bbc.co.uk/schools/ks2bitesize/science/physical_processes.shtml