You push an air-hockey puck along a surface with negligible friction while riding in a truck as it moves at a constant velocity in Earth's frame of reference. What do you observe? Why?
I'm tempted to say that the puck moves forward because that's all I can think of, but I really don't think that's right; there should be more to it... :(
You are correct that there is more to it! When you push the air-hockey puck along the surface while riding in the truck, you will observe the puck's motion relative to your position inside the truck. Since there is negligible friction between the puck and the surface, and the truck is moving at a constant velocity, the puck will glide smoothly across the surface in the direction you pushed it.
This observation can be explained through the concept of Galilean relativity, which states that the laws of motion are the same in all inertial frames (frames of reference that are not accelerating). Since both you and the air-hockey puck are inside the truck, which is an inertial frame in this case, the puck will move in a straight line with a constant velocity, relative to the truck and you, until it is stopped by an external force (like hitting the edge of the air-hockey table).
If someone were to observe the situation from outside the truck, however, they would see the air-hockey puck moving forward with the combined velocities of the truck and the velocity it gained from your push. This is because, in Earth's frame of reference, the puck's motion will be influenced by the truck's motion as well.
When you push an air-hockey puck along a surface with negligible friction, while riding in a truck that moves at a constant velocity in Earth's frame of reference, you will observe the puck moving forward at a constant speed. This observation is based on Newton's first law of motion, also known as the law of inertia.
Newton's first law states that an object at rest remains at rest, and an object in motion continues to move at a constant velocity unless acted upon by an external force. In this case, when you push the puck, it starts moving forward. Since the friction on the surface is negligible, there is no significant force acting on the puck to slow it down. Additionally, the constant velocity of the truck does not exert any force on the puck in the direction of the truck's motion.
Therefore, the puck continues to move forward at a constant speed, unaffected by the motion of the truck. This is known as the principle of relative motion – the motion of an object is measured relative to a particular frame of reference, in this case, the Earth's frame of reference.
When you push an air-hockey puck along a surface inside a truck that is moving at a constant velocity in Earth's frame of reference, you would observe that the puck continues to move forward with the same speed and direction relative to you and the truck. This is because, in the absence of any significant friction, the puck will not experience any force that could change its state of motion.
From your frame of reference (inside the truck), both you and the puck are in the same inertial reference frame because you are moving at the same constant velocity. In this frame, there are no forces acting on the puck in the horizontal direction since you are neglecting friction.
According to Newton's first law of motion, an object in motion will continue to move in a straight line at a constant velocity unless acted upon by an external force. In this scenario, the puck is already moving at a constant velocity due to the initial push, and there are no additional forces acting on it to change that motion.
However, it is important to note that from an observer outside the truck or in a different inertial reference frame, such as someone watching the truck from the side of the road, they would see the puck moving not only forward but also backward due to the truck's motion. This is because they are observing the puck from a different frame of reference where the truck's constant velocity is accounted for.
In summary, when you push an air-hockey puck along a surface inside a truck that is moving at a constant velocity in Earth's frame of reference, you would observe the puck continuing to move forward with the same speed and direction relative to you and the truck due to the absence of significant friction.