Understanding how forces act on objects is an important physics concept. You will need to understand how forces act on objects to understand basic physics concepts such as Newton’s laws of motion and gravity.
Forces can be imagined as a pulling or pushing force. There are two types of forces: direct and indirect. A direct force is the pull or push caused by something directly affecting an object, like putting a weight on a scale. An indirect force is a pull or push caused by something else, like when the wind blows and pushes against a tree.
When figuring out how a object is affected by a force, you must determine the direction of the net force acting on the object at position A. Net force is the total force acting on an object, minus the opposing force acting on it.
Calculate the direction of the object’s acceleration
The next step is to calculate the direction of the object’s acceleration. An object’s acceleration is the change in its velocity over time.
Velocity is how fast an object moves, so how can there be a change in velocity?
A change in an object’s position is what defines its velocity. If an object does not change its position, then it has no velocity.
So how do we calculate the acceleration of an object? You divide the net force by the mass of the object. The net force is the force that remains after subtracting all other forces.
For example, if there are two forces acting on an object, one that pulls it left and one that pulls it right, but there is no force pulling it up or down, then the net force is equal to zero and the only acceleration will be due to left and right movements.
Consider what happens when an object moves in a straight line at constant speed
If an object moves in a straight line at constant speed, the net force on the object is zero. Constant speed means that the speed of the object does not change over time; it maintains a constant value.
Constant speed also means that the direction of the object’s velocity does not change over time. Velocity is how we describe motion in a particular direction.
If you draw a vector diagram to represent this situation, you will find that all of the forces acting on the object are in sync and equal in magnitude, so they do not produce any net force. The object is moving at constant speed, so there is no acceleration.
At Position A in Figure 1, no net force acts on the ball because all of the forces acting on it are parallel to each other.
Consider what happens when an object moves in a circle at constant speed
Imagine that you are standing at point A in the figure above. You notice that there is a tangent force acting on the object at point A.
Because you are aware of this tangent force, you can assume that there is also a net force acting on the object at point A. By definition, the net force acting on an object is the sum of all forces acting on it.
Since there is no change in speed or direction at point A, you can assume that the direction of the net force is zero. only gravity acts opposite to the direction of motion, so only gravity contributes to the net force at point A.
Now imagine that you are standing at some other position B anywhere outside of the circle. You notice that there is no tangent force acting on the object at position B. Therefore, by definition, there is no net force acting on the object at position B.
What does Newton’s first law say about the direction of the net force acting on an object?
The net force acting on an object is the sum of all forces acting on the object. As explained above, a force is something that causes an object to change its velocity (or speed and direction) .
If there is a force acting on an object, then there must be a change in velocity. In other words, if there is a force on an object, that object will either change its speed or its direction of motion.
The magnitude of the net force determines the direction of the change in velocity. If the net force is positive, then the object will accelerate in the direction of the net force. If the net force is negative, then the object will accelerate in the opposite direction.
At any given time, there are many forces acting on an object, so its velocity may be changing due to these various forces.
Does this mean that if I drop something, it will fall down and not sideways or up?
No, that is not the case. This question is related to another physics concept called velocity.
Velocity is the speed at which an object moves in a given direction. When we talk about falling objects, we are talking about the velocity of the object.
The trick is that velocity is a vector quantity. This means that it has a direction as well as a magnitude (size).
So, even though the net force acting on an object at position A is down, the object will still move in any other direction due to its velocity being other than zero.
If you drop an object and it does not hit anything else before landing, then yes, it will land on the ground. But if it hits something else first, then it may change its direction due to the impact.
What are some examples where objects move at different speeds?
Every day, you interact with objects that move at different speeds. You walk into a room, but the other side of the room is moving away from you at a different speed than you are moving.
The floor is also moving beneath you, which means you are also moving in relation to the floor. The ground is also moving, which means you are also moving in relation to the ground.
Vehicles such as cars and trains operate on the same principle. The wheels move the car or train forward, but it must first move in relation to the ground it is traveling on.
Whether an object moves at a constant speed or changes speed depends on its internal forces acting upon it. When there are no external forces acting upon an object, it will not change speed. Only force can change the velocity of an object.
What are some examples where objects move in curved paths?
Many objects move in curved paths every day. For example, when you wash your hair with shampoo, the shampoo moves down the length of your hair to the bottom of the shower where it collects as a result of gravity.
Soap bubbles also move in curved paths when you poke them. When you poke a soap bubble, a force is applied to it that pushes it away from you. Because of this force, the bubble moves in a different direction than what it was originally moving in.
Both of these examples show that objects move in curved paths because of forces acting on them. Gravity is the force that causes objects to move down the shower drain or bounce off of each other. Soap bubbles are lighter than air, so they are pushed away from where they were originally moving by air pushing back on them.
How do I find the total net force on an object?
You can find the total net force on an object by adding all of the forces acting on it and then subtracting the forces acting in the opposite direction.
For example, imagine that there is a ball sitting on a floor and there is a force pushing down on the ball from the floor (via gravity) and a force pulling up on the ball from a string attached to it.
There is a net force of gravity pulling down on the ball, so it will move in that direction. However, there is also a net force of pullup on the ball, so it will also move in that direction.
To figure out which way it will move, you have to determine which direction the pullup force is going. If you determine that it is going right, then the ball will also move in that direction.