Define the term momentum.

Here are the answers to the questions:

1. a) Momentum is defined as the product of an object's mass and its velocity. It is a vector quantity, meaning it has both magnitude and direction.

   $$\boxed{\text{Momentum} = \text{mass} \times \text{velocity}}$$

   b) The device used to measure atmospheric pressure is a barometer.

2. a) Two properties of an ideal gas are:

   • The particles of an ideal gas have negligible volume compared to the volume of the container.
   • There are no intermolecular forces of attraction or repulsion between the particles of an ideal gas.

   b) The principle behind the construction of a simple hydrometer is Archimedes' principle. This principle states that the buoyant force on an object submerged in a fluid is equal to the weight of the fluid displaced by the object. A hydrometer floats higher in denser liquids and lower in less dense liquids.