Definition 3.6.1. The Gravitational Force.
The gravitational force on a system with mass \(m_A\) in the presence of a gravitational field \(\vec{g}_B\) is:
\begin{equation*}
\vec{F}^{G}_{AB} = m_A\vec{g}_B
\end{equation*}
Section 3.6 The Gravitational Force
The gravitational force uses a form that is common in physics: a product of a property of the system feeling the force (here, mass \(m_A\)) and a property of the system exerting the force (here, gravitational field \(\vec{g}_B\)). This aligns with the general model for forces, which always involves two systems! Interestingly, gravity is a non-contact force: it will act on a system even if no other system is in contact with it.
Exercises Activities
1. Summarize What You Learned - Gravitational Field.
At the end of the video, you are asked to think about what kind of quantity the gravitational field is. Take a moment to think about the name, symbol, and equation. Then, write down 2-3 things you think might be true for the gravitational field.
2. Sensemaking - Equations.
The equation for the gravitational force given above looks a lot like the Law of Motion: \(\vec{F}_{net} = m\vec{a}\text{.}\) However, these two equations are not the same. Identify at least two differences between the equations.
3. Sensemaking - Units.
What are the units of the gravitational field? What do you think the units mean here?
Answer.
Either N/kg or m/s\(^2\text{.}\)
4. Practice - Gravitational Field.
Your friend claims they have a gravitational field generator that can create a gravitational field throughout their physics lab. You decide to test it by placing a 12 kg object in the lab and measuring a gravitational force with magnitude 7.8 N acting on the object. What is the magnitude of the gravitational field your friend has created?
Answer.
0.65 N/kg
