题干

如图将物理课本按在教室垂直的墙壁上,课本正在匀速下滑,下列说法正确的是(  )

A:课本只受重力和手对它的压力

B:若将课本按在较光滑的窗玻璃上,课本也匀速下滑,则手对它的压力与之前一样大

C:增加手对课本的压力,课本所受摩擦力会增加

D:放手之后,课本所受摩擦力不变

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答案(点此获取答案解析)

C

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    Family Fun in Canadian Museum of Nature

    Bring the whole family to rediscover our fully reformed museum and new galleries.

    What to See and Do

    Check out What's On for all the events, educational activities and HD movies happening during your visit. On the first floor, you can see birds, dive down into the depths at the helm(舵柄)of a submersible(潜水器)or explore a cave. Don't miss our 3D gallery play areas on the third floor when visiting with kids. By visiting here, your children will learn more about nature. Check out Our Exhibitions which presents our special exhibitions.

    Hours, Admission, Services and More

    Everything you need to plan your visit:

    Opening Hours

    Summer Hours (June1—September 4):

    9am-6pm(Saturday—Wednesday)

    9am-8pm(Thursday and Friday)

    Regular Hours: 9am-5pm(except Monday and Thursday)

    Admission

    Adult: $14

    Senior(65+):$12

    Student (13+):$12

    Child(3-12):$10

    Tiny Tot(0-2):Free

    Parking

    Paid parking is available on the Canadian Museum of Nature grounds.

    Rates

    $3 per half hour

    At most $14 per day(until 4:30 am)

    Evening flat rate(统一价格):

    $5(4:30pm-4:30 am)

    Charges accumulate(evening and next day)of vehicles that are parked overnight.

    Shopping

    Be sure to stop at our Nature Boutique on the second floor for a vast selection of games, books and nature-related souvenirs.

    Explore Nature

    The Canadian Museum of Nature provides a lot of information, images and videos on our websites. The museum participates in several social networks. Follow us on Facebook, YouTube, Instagram and Twitter.