Topic 2.2: Forces II

Question 1

What is mass?

Answer 1

Mass is the amount of matter in a body

Question 2

What is weight?

Answer 2

Weight is the force due to gravity acting on a mass

Question 3

What happens when in moving upwards in an elevator?

Answer 3

When accelerating upwards we feel heavier, however our ‘weight’ or gravitational force does not change

Question 4

Why do we feel like that in an elevator?

Answer 4

We feel pushed into the floor due to our inertia, the floor is accelerating upwards while our body is stationary at the start

Question 5

What are fours ways we can be weightless?

Answer 5

1. When we are infinitly long away from a planet/star etc.
2. In a free falling elevator
3. In orbit travelling at constant speed
4. In a spacecraft with the engines off either
   a. moving towards a planet (increasing acceleration)
   b. moving away from a planet (decreasing acceleration)

Question 6

What is friction?

Answer 6

A force that opposes motion

Question 7

How are the frictional force and the pulling force correlated?

Answer 7

If the pulling force is zero, friction is zero. If the pulling force is slowly increased, the frictional force F wwill increase up until a maximum value

Question 8

What is the formula for the coefficent of static friction?

Answer 8

μ ≥ F / R

Question 9

What are the rules for the coefficent of static friction?

Answer 9

μ (coefficient of static friction) is always less than 1 and only depends on the two materials in contact

Question 10

What happens when the pulling force is great enough for the body to start moving?

Answer 10

When the pulling force is great enough the body will start to move. The frictional force decreases when it’s moved. We now have to consider the coefficent of dynamic friction

Question 11

What is the formula for dynamic friction?

Answer 11

μ = F / R