# Determining the greater force?

• B
• Amelina Yoo
In summary, Fred would have to apply the larger force in both scenarios. This is due to the difference in gravity between Earth and the Moon, with Earth having a greater gravitational force and thus requiring more force to lift or throw an object. However, in the second scenario, if atmospheric resistance is taken into account, there may be a larger force needed for Fred to throw the rock horizontally. Additionally, both Fred and Jane would need to apply a vertical force equal to the weight of the rock in order to achieve horizontal velocity.

#### Amelina Yoo

Q: Fred is on Earth, and Jane is on the Moon.

a) Each lifts a 2.0 kg rock. Who has to apply the larger force?
b) Each throws the rock horizontally with initial speed of 6.0 metres per second. Who applies the larger force?

For both questions, I wrote: Fred, because the gravity on Earth is greater than that of the Moon, and so there is a larger force acting upon the rock. But, seeing as it is my answer to BOTH question, I am feeling doubtful, because how can there be the same answer to two questions?

Amelina Yoo said:
a) Each lifts a 2.0 kg rock. Who has to apply the larger force?
I believe you're right, it's Fred.
Amelina Yoo said:
b) Each throws the rock horizontally with initial speed of 6.0 metres per second. Who applies the larger force?
If atmospheric resistance is to be taken into account, I believe it should be Fred. If not, I think both will apply equal force. The rock will take longer to land on moon.

The second question does not have a good answer, as it is asked.
Even without leaving our planet you can achieve the 6 m/s speed of the rock with any force. It just depends on how long it takes to accelerate the rock.
Of course, besides the horizontal force, you need to apply a vertical force equal to the weight of the rock, in every case.
So assuming that both use the same horizontal force, for the same amount of time, the total force will be larger on Earth.

Regarding your concern, there is no rule to rule out same answer to two different questions.

Amelina Yoo said:
Q: Fred is on Earth, and Jane is on the Moon.

a) Each lifts a 2.0 kg rock. Who has to apply the larger force?
b) Each throws the rock horizontally with initial speed of 6.0 metres per second. Who applies the larger force?

For both questions, I wrote: Fred, because the gravity on Earth is greater than that of the Moon, and so there is a larger force acting upon the rock. But, seeing as it is my answer to BOTH question, I am feeling doubtful, because how can there be the same answer to two questions?
To throw a rock requires applying force over a distance, or work, on the rock. Work is the dot product of force and displacement. There is no extra force due to gravity horizontally therefore the dot product does not vary with gravity. Therefore, both use the same force (assuming it takes the same amount of time to throw).

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Lifting a rock in lower gravity requires less force. Accelerating a given mass in a direction perpendicular to any gravitational field requires the same force.

If you want to have horizontal velocity at the end of acceleration you need to exert a vertical force as well. Otherwise the rock falls during the acceleration period and the final velocity won't be horizontal. The question in the OP does not specify that is about the horizontal component of the force only.

## 1. What is meant by "greater force" in scientific terms?

The greater force refers to the stronger or more dominant force acting on an object or system. This can be determined by comparing the magnitudes and directions of different forces.

## 2. How do you measure and determine the greater force?

The greater force can be determined by using a force meter or scale to measure the magnitude of each force and then comparing the values. The direction of each force also needs to be taken into account, as forces in opposite directions can cancel each other out.

## 3. What factors affect the determination of the greater force?

The determination of the greater force can be affected by the magnitude and direction of each force, as well as the mass and acceleration of the object or system being acted upon. Other factors such as friction, air resistance, and external forces can also impact the determination.

## 4. Can the greater force change over time?

Yes, the greater force can change over time as the magnitudes and directions of forces acting on an object or system can vary. For example, if an additional force is applied or an existing force changes in magnitude or direction, the greater force may also change.

## 5. Why is it important to determine the greater force in scientific experiments?

Determining the greater force is important in scientific experiments as it helps to understand the overall motion and behavior of objects or systems. It also allows for accurate predictions and calculations of forces and their effects, which can be crucial in various fields such as engineering, physics, and mechanics.