A force causes an object to undergo a specific change. Unbalanced forces cause changes in speed, shape, or direction. Gravitational force acts between masses. Friction opposes motion.

forces acting on an object can change the shape of the object, the speed of the object, and the direction in which the object is moving

the direction of the object's acceleration is the same as the direction of the unbalanced force

the magnitude of the object's acceleration varies in direct proportion with the size of the unbalanced force

the magnitude of the object's acceleration varies inversely with the mass of the object

When two surfaces slide past each other, the interaction between them produces a force of friction

Weight is not the same as mass. Mass is a measure of how much matter is in an object. Weight is a force acting on that matter. Mass resists any change in the motion of objects

In physics, the term weight has a specific meaning - which is the force that acts on a mass due to gravity. Weight is measured in newtons. Mass is measured in kilogram

The mass of a given object is the same everywhere, but its weight can change. We use balances to measure weights and masses

example: sliding a hockey puck on ice will eventually stop because there is friction on ice. It will also stop if it hits something, like a player's stick or goalspot

example: riding a bike. the mass is the bike, and the force is our leg muscles pushing the pedals of the bike is the force. When we push on the pedals, the bike accelerates. We are increasing the speed of the bike by applying force to the pedals.

example: jumping. When we jump, our legs apply a force to the ground, and the ground applies an equal and opposite reaction force that launches us into the air