Chapter 25. Newton’s first law of motion (4-6)

Question

FIbmRaNubKQH9HpTDLj7Ke/migpuzQJCwhGtbltOvI+Q7z++Ct3/SHoAnDbeozR0QSHd9zRlxWE=
{"title":"If the net external force on an object is zero...","description":"Correct!","type":"correct","color":"#99CCFF","code":"[{\"shape\":\"poly\",\"coords\":\"82,133\"},{\"shape\":\"rect\",\"coords\":\"10,16,12,16\"},{\"shape\":\"poly\",\"coords\":\"144,22\"},{\"shape\":\"rect\",\"coords\":\"36,5,53,27\"}]"} {"title":"...the object does not accelerate...","description":"Incorrect","type":"incorrect","color":"#ffff00","code":"[{\"shape\":\"rect\",\"coords\":\"131,9,151,28\"}]"} {"title":"...and the velocity of the object remains constant. If the object is at rest, it remains at rest; if it is in motion, it continues in motion in a straight line at a constant speed.","description":"Incorrect","type":"incorrect","color":"#00ff00","code":"[{\"shape\":\"rect\",\"coords\":\"206,9,224,26\"}]"}

Question

ab1BS91bTTL4vCr6GpKOastL4IDEDvSe/BZD0tzrrxwmX7SScxpfAw==
{"title":"If the net external force on an object is zero...","description":"Wrong","type":"incorrect","color":"#99CCFF","code":"[{\"shape\":\"poly\",\"coords\":\"82,133\"},{\"shape\":\"rect\",\"coords\":\"10,16,12,16\"},{\"shape\":\"poly\",\"coords\":\"144,22\"},{\"shape\":\"rect\",\"coords\":\"36,5,53,27\"}]"} {"title":"...the object does not accelerate...","description":"Correct!","type":"correct","color":"#ffff00","code":"[{\"shape\":\"rect\",\"coords\":\"131,9,151,28\"}]"} {"title":"...and the velocity of the object remains constant. If the object is at rest, it remains at rest; if it is in motion, it continues in motion in a straight line at a constant speed.","description":"Incorrect","type":"incorrect","color":"#00ff00","code":"[{\"shape\":\"rect\",\"coords\":\"206,9,224,26\"}]"}

Question

wOOT+cKlFjYu0Mu0oly3kgm30tOQx6FYOGa9G2lTMWN6pjfBO7eNWdMl1r/6Wi4wv+yfCP/joIa2eyQMgros2AHxuA1Le13qoSpmqt/IvKMnt38sKsWP13jMNAgHTbPJgWcad+RTFfj3NznpHIxt5A11YIjVLNbQ+lOA0KXtWowJIi01y5Woe4xIRfwv0uqK9Q+9jKGsxzkgSQb99nrgvULOMcWb407RLAZjJn3RP2fbCFFHWDi7Ow==
{"title":"If the net external force on an object is zero...","description":"Wrong","type":"incorrect","color":"#99CCFF","code":"[{\"shape\":\"poly\",\"coords\":\"82,133\"},{\"shape\":\"rect\",\"coords\":\"10,16,12,16\"},{\"shape\":\"poly\",\"coords\":\"144,22\"},{\"shape\":\"rect\",\"coords\":\"36,5,53,27\"}]"} {"title":"...the object does not accelerate...","description":"Incorrect","type":"incorrect","color":"#ffff00","code":"[{\"shape\":\"rect\",\"coords\":\"131,9,151,28\"}]"} {"title":"...and the velocity of the object remains constant. If the object is at rest, it remains at rest; if it is in motion, it continues in motion in a straight line at a constant speed.","description":"Correct!","type":"correct","color":"#00ff00","code":"[{\"shape\":\"rect\",\"coords\":\"206,9,224,26\"}]"}

Review

You’re on a train in the station, looking out the window at the train right next to yours. One of the trains is moving, but you can’t tell which (Figure 25-2). Is your train moving and the other one stationary, or vice versa? Perhaps both are moving. How can you tell?

To address this question, let’s return to Newton’s first law, which we introduced in Section 4-3:

The first law states that an object that experiences no net force could either be at rest or in motion at a constant velocity. Newton’s laws therefore treat both cases identically. So although we might make a distinction between an object at rest and one in (uniform) motion with respect to us, the laws of physics do not. In the case of the two trains, this tells us something profound: If you have no reference to the ground or the tracks on which the trains move, there is no way to design an experiment or make a measurement that would tell you whether the other train is moving at a constant velocity with respect to yours or your train is moving a constant velocity with respect to the other one.