"tug at" or "tug on"?

Her fingers tugged at the cord above her head.

She seemed to tug at it, gave a little grunt of exertion.

Tugging at the purse strings always gets peoples ' attentions.

Grant all about it when a swirl of the falling tide made the cutter dance and tug at her moorings.

A deep-side part looks fresh and modern (and is easy to do when the kids are tugging at your arm!).

Rufus, who was now gnashing his teeth and tugging at his hair, quickly turned the basketariot around.

He kept his gaze on his hands in his lap, and twitched when Xavi tugged at his chin, trying to get him to turn around.

Remember how you and your husband met? What tugged at your heart about him? Chances are those characteristics still run strong in your man.

Use your lips to tug on hers and slightly bite on her lips at the same time.

In doing your facials be careful not to tug on the eye area, which is delicate.

The stories of these ' superhumans ', as dubbed by channel 4, tugs on your heart strings and you can't help but feel drawn and compelled to them.

He tugged on the tail and sleeves of his jacket to make it as presentable as possible and patted his pocket to make sure the package he was delivering was still secure.

It's also not a gas giant like Jupiter and Saturn, it is a large planet tugging on the sun and interacting with the potential of other planetary mass in the solar system.

A lawyer herself, she's in constant, animated conversation with her father during breaks, and with worry written all over her face, twists and tugs on her hair during testimony.

To chase the orbit of a comet back through time is not such an easy task as it might sound, for the gravitational effects of the planets are perpetually tugging on the comet and modifying its orbit.

The following dialogue begins just after he has shared with me -- quite out of the blue -- that he once went to a rub and tug by accident.

The ship, which was first launched in 1797, is stationed in Charlestown, and periodically is tugged into the harbour for historical display.

This is because a minimoon would not be tightly held by Earth's gravity, so it would be tugged into a crazy path by the combined gravity of Earth, the Moon and the Sun.