Eddie Butler pitched a bullpen session Wednesday as thousands of chatty kids around him at Coors Field played with rubber bands. It was weather-and-science day at the ballpark, and a teacher in a lab coat was talking about physics.

“Pitchers know a way to throw the ball that makes it harder to hit,” Butler overheard the teacher say. The kids unspooled two cups taped together with the flick of a rubber band, and the cups floated away.

“They make things trickier by throwing a curveball,” the teacher said.

It’s not that simple.

Butler’s lesson in Coors Field physics has a much steeper learning curve. The 25-year-old right-hander and fellow first-round draft pick Jon Gray, 24, are still taking notes on how to pitch well at altitude.

Gray and Butler, after gaining traction with superb outings on a successful Rockies road trip through the West Coast last week, return home to pitch back-to-back games Friday and Saturday against the defending National League champion New York Mets. Their ERAs will be tested.

“Physics was always fun for me, talking about mass velocity and the change of it,” Butler said. “We pitchers understand physics. We can’t always put it into words — but we understand it because we deal with it day in and day out.”

Butler, for the first time since he was called up from Double-A two years ago — then sent down twice — has found some footing. In 14 innings this season, he has given up six runs, posting 13 strikeouts against three walks. In his last outing, he pitched six scoreless innings at San Francisco, outdueling the Giants’ Jeff Samardzija.

Gray has done even better, with 28 strikeouts and just six walks over 21 innings. He pitched seven one-hit, no-run innings at San Francisco last week. That came after he struck out 11 and walked just one in San Diego against the Padres.

Those were all road starts. But Butler and Gray — like nearly every pitcher in a Rockies uniform — have found trouble translating pitches at altitude in their young careers.

This time, they said, there’s no reason to worry.

“I don’t think it will play in my mind as much as it has,” said Gray, a rookie. “I’m going to treat it the same and make pitches and get groundballs. I don’t need to treat it any differently. There are going to be some more things, like, ‘OK, I’m going to start my curveball a little lower’ or my slider a little more left. But it won’t be a big issue.”

Gray and Butler have pitched to wildly different results at Coors Field and away from Denver. Gray has a 2.18 ERA on the road, compared with 9.20 at home; batters have hit .184 against him on the road, .394 at home. Butler has a 5.18/6.65 road-home ERA split and .289/.343 batting average against.

Coors Field remains their bane. The Rockies are 5-10 at Coors Field when Butler or Gray start.

“You have to be adaptable and be able to change on the fly,” Butler said.

For both of them, that means changing their sights. The Coors Field effect on pitchers is most severe when they pitch right after returning from a road trip. That forces them to pitch an off-day bullpen session on the road, then a game at home.

Butler and Gray this week, though, threw their bullpen sessions at Coors Field. They said that helps.

“The first guy, the first two guys who have to pitch after a road trip, that’s tough,” Butler said, “because you were throwing in dense air where the ball moved a lot and then your first day throwing here, you have to make it happen on the mound.”

Butler moved away from the changeup and he’s throwing a slider with 31.1 percent of his pitches, nearly double his career mark. Batters are swinging and missing at that slider more than half the time. Butler is striking out 24.1 percent of batters he faces this year, more than double his career average, while walking just 5.6 percent, less than half his career mark.

Gray, too, is showing a more lively pitch arsenal. He’s throwing a slider 33.1 percent of the time (up by 14 percent) and a new curveball (2.2 percent) as his off-speed pitches, instead of a changeup (down to 3.8 percent from 17.1), according to PITCHf/x.

“I’m just going to stick to my strengths, find my rhythm in the first inning and try to cruise from there,” Gray said. “Make pitches and work quick.”

Nick Groke: ngroke@denverpost.com or @nickgroke

Looking ahead

Mets RHP Matt Harvey (3-4, 4.50 ERA) at Rockies RHP Jon Gray (0-1, 5.40), 6:40 p.m. Friday, ROOT; 850 AM

Even a one-hitter over seven innings against the Giants in San Francisco last week couldn’t get Gray his first career victory. He left with the score tied, and the Rockies ended up losing 2-1 in 13 innings. He still hasn’t won a major-league game, but some of it is out of his control. The Rockies are 1-3 in games Gray has started this season, but they’ve scored just two runs total in his past two starts. There are better numbers to illustrate how Gray is pitching. He has a 2.12 xFIP (fielding independent pitching), according to Fangraphs, an ERA-type number that strips away factors out of a pitcher’s control, such as defense and ballpark effects. If he had enough innings to qualify, he would rank second in baseball behind only Dodgers star Clayton Kershaw. Nick Groke, The Denver Post

Saturday: Mets RHP Logan Verrett (3-0, 1.27 ERA) at Rockies RHP Eddie Butler (1-1, 3.86), 6:10 p.m., ROOT

Sunday: Mets RHP Jacob deGrom (3-1, 2.12) at Rockies RHP Tyler Chatwood (4-3, 3.09), 2:10 p.m., ROOT

Monday: Off

Tuesday: Rockies LHP Chris Rusin (1-1, 4.85) at Cardinals LHP Jaime Garcia (3-2, 2.58), 6:15 p.m., ROOT