```r
physics %>% 
  filter(str_detect(text, "K1")) %>% 
  select(text)
```

```
## # A tibble: 59 x 1
##    text                                                                  
##    <chr>                                                                 
##  1 to a second co-ordinate system K1 provided that the latter is         
##  2 condition of uniform motion of translation. Relative to K1 the        
##  3 tenet thus: If, relative to K, K1 is a uniformly moving co-ordinate   
##  4 with respect to K1 according to exactly the same general laws as with 
##  5 does not hold, then the Galileian co-ordinate systems K, K1, K2, etc.,
##  6 Relative to K1, the same event would be fixed in respect of space and 
##  7 to K1, when the magnitudes x, y, z, t, of the same event with respect 
##  8 of light (and of course for every ray) with respect to K and K1. For  
##  9 reference-body K and for the reference-body K1. A light-signal is sent
## 10 immediately follows. If referred to the system K1, the propagation of 
## # … with 49 more rows
```