Question

unit 2: forces at a distance
fill in the blank with the correct words.

1. a force that acts without touching an object, such as gravity, is called a field force.
2. the force of attraction between two objects that have mass is known as
3. the acceleration due to gravity on earth is approximately m/s².
4. magnetism is a force caused by certain and can push or pull on objects.
5. the law of universal gravitation depends on an object’s and the between objects.

choose the correct answer from the choices for each question.

1. which of the following is an example of a contact force?

a) gravity
b) electrostatic force
c) friction
d) magnetism

1. what happens to the gravitational force between two objects if their masses increase?

a) it decreases
b) it disappears
c) it stays the same
d) it increases

1. on which planet would an astronaut weigh the most?

a) earth
b) mars
c) jupiter
d) venus

1. what is the main difference between contact forces and field forces?

a) contact forces act only in water, field forces act in air
b) field forces are weaker than contact forces
c) contact forces require touching, field forces do not
d) contact forces are invisible

1. according to kepler’s first law, the orbits of planets are shaped like:

a) squares
b) ovals
c) triangles
d) perfect circles

Explanation:

Step1: Recall gravitational - force concept

The force of attraction between two objects that have mass is called gravitational force.

Step2: Know acceleration - due - to - gravity value

The acceleration due to gravity on Earth is approximately 9.8 m/s².

Step3: Understand magnetism source

Magnetism is a force caused by certain materials (magnetic materials) and can push or pull on objects.

Step4: Recall law of universal gravitation

The Law of Universal Gravitation depends on an object's mass and the distance between objects.

Step5: Identify contact - force

Friction is a contact force as it acts when two surfaces are in contact. Gravity, electrostatic force, and magnetism are field forces.

Step6: Analyze gravitational - force and mass relation

According to the Law of Universal Gravitation $F = G\frac{m_1m_2}{r^{2}}$, when the masses $m_1$ and $m_2$ increase, the gravitational force $F$ increases.

Step7: Consider planet's gravitational - strength

Jupiter has the largest mass among the given planets. According to $F = mg$ (where $g$ is the gravitational - acceleration of the planet), an astronaut would weigh the most on Jupiter.

Step8: Differentiate contact and field forces

The main difference between contact forces and field forces is that contact forces require touching, while field forces do not.

Step9: Recall Kepler's First Law

According to Kepler's First Law, the orbits of planets are shaped like ovals (ellipses).

Answer:

1. Gravitational force
2. 9.8
3. Materials
4. Mass; distance
5. c) Friction
6. d) It increases
7. c) Jupiter
8. c) Contact forces require touching, field forces do not
9. b) Ovals